Report on the Radiolaria Collected by H.M.S. Challenger During the Years 1873-1876, First Part: Porulosa (Spumellaria and Acantharia) / Report on the Scientific Results of the Voyage of H.M.S. Challenger During the Years 1873-76, Vol. XVIII

Previous
Ernst Haeckel

Legion I. SPUMELLARIA ,

Legion II. ACANTHARIA ,

Title: Report on the Radiolaria Collected by H.M.S. Challenger During the Years 1873-1876, First Part: Porulosa (Spumellaria and Acantharia)

Report on the Scientific Results of the Voyage of H.M.S. Challenger During the Years 1873-76, Vol. XVIII

Author: Ernst Haeckel

Language: English

Character set encoding: ISO-8859-1

E-text prepared by
Charlene Taylor, Adrian Mastronardi, Keith Edkins,
and the Online Distributed Proofreading Team
(http://www.pgdp.net)
from page images generously made available by
Internet Archive
(https://archive.org)

Transcriber's note: Some typographical errors in the printed work have been corrected. The corrected text is underscored in red like this. Hover the cursor over the marked text and the explanation should appear. The Addenda & Errata (Second Part, pp. 1763-4) have been applied and underscored in this way.

REPORT

ON THE

SCIENTIFIC RESULTS

OF THE

VOYAGE OF H.M.S. CHALLENGER

DURING THE YEARS 1873-76

UNDER THE COMMAND OF

Captain GEORGE S. NARES, R.N., F.R.S.

AND THE LATE

Captain FRANK TOURLE THOMSON, R.N.

PREPARED UNDER THE SUPERINTENDENCE OF

THE LATE

Sir C. WYVILLE THOMSON, Knt., F.R.S., &c.

REGIUS PROFESSOR OF NATURAL HISTORY IN THE UNIVERSITY OF EDINBURGH

DIRECTOR OF THE CIVILIAN SCIENTIFIC STAFF ON BOARD

AND NOW OF

JOHN MURRAY

ONE OF THE NATURALISTS OF THE EXPEDITION

Zoology—Vol. XVIII.

FIRST PART

Published by Order of Her Majesty's Government

PRINTED FOR HER MAJESTY'S STATIONARY OFFICE

AND SOLD BY

LONDON:—EYRE & SPOTTISWOODE, EAST HARDING STREET, FETTER LANE

EDINBURGH:—ADAM & CHARLES BLACK

DUBLIN:—HODGES, FIGGIS, & CO.

1887

Price (in Two Parts, with a Volume of Plates) £5, 10s.

CONTENTS.

Report on the Radiolaria collected by H.M.S. Challenger during the years
1873-1876.

By Ernst Haeckel, M.D., Ph.D., Professor of Zoology in the University of Jena.

FIRST PART.—PORULOSA.

(SPUMELLARIA AND ACANTHARIA.)

EDITORIAL NOTES.

The Report on the Radiolaria by Professor Ernst Haeckel of Jena occupies the whole of the present Volume, the text being bound up in Two Separate Parts and the Plates in a Third Part. The Report forms Part XL. of the Zoological Series of Reports on the Scientific Results of the Expedition, and is the largest single Report of the series which has up to this time been published.

The Manuscript of the Systematic Part was written by Professor Haeckel in the English language, and was received by me in instalments on the 12th August 1884, 13th July and 4th December 1885, and 3rd June 1886. The Introduction was written in German and was translated into the English language by Mr. W. E. Hoyle of the Challenger Editorial Staff; the German text being received in instalments between the 15th July 1886, and the 25th January 1887.

The Challenger Naturalists found the representatives of this group of animals to be universally distributed throughout ocean waters, and their dead remains to be nearly equally widely distributed over the floor of the ocean, the relative abundance and the species differing, however, with change of locality, and their abundance or variety being intimately connected with some of the most interesting and intricate problems of general oceanography.

It was a fortunate circumstance that so distinguished a Naturalist, with such an intimate knowledge of the Radiolaria, should have been willing to undertake the laborious examination and description of the extensive collections made during the Expedition. Professor Haeckel has devoted ten years of his life to this work, and this Report sets forth the results of his labours, on the conclusion of which he will be congratulated by all Naturalists. The entire literature of the Radiolaria (from 1834 to 1884) is completely recorded, and the older species (both living and fossil) redescribed, so that the Report is a complete Monograph, which will be an invaluable aid to all future Investigators.

"John Murray.

Challenger Office, 32 Queen Street,

Edinburgh, 1st February 1887.

THE

VOYAGE OF H.M.S. CHALLENGER.

ZOOLOGY.

Report on the Radiolaria collected by H.M.S. Challenger during the Years 1873-76. By Ernst Haeckel, M.D., Ph.D., Professor of Zoology in the University of Jena.

PREFACE.

The significance of the Radiolaria in regard to the relations of life in the ocean has been increased in a most unexpected manner by the discoveries of the Challenger. Large swarms of these delicate Rhizopoda were found not only at the surface of the open ocean but also in its different bathymetrical zones. Thousands of new species make up the wonderful Radiolarian ooze, which covers large areas of the deep-sea bed, and was brought up from abysses of from 2000 to 4000 fathoms by the sounding machine of the Challenger. They open a new world to morphological investigation.

When ten years ago (in the autumn of 1876) I accepted the enticing invitation of Sir Wyville Thomson to undertake the investigation of these microscopic creatures, I hoped to be able to accomplish the task with some degree of completeness within a period of from three to five years, but the further my investigations proceeded the more immeasurable seemed the range of forms, like the boundless firmament of stars. I soon found myself compelled to decide between making a detailed study of a selection of special forms or giving as complete a survey as possible of the varied forms of the whole class; and I decided upon the latter course, having regard both to the general plan of the Challenger Reports, and to the interests of our acquaintance with the class as a whole. I must, however, confess at the close of my work that my original intention is far from having been fulfilled. The extraordinary extent and varied difficulties of the undertaking must excuse the many deficiencies.

The special examination of the Challenger collection was for the most part completed in the summer of 1881; I collected its results in my Entwurf eines Radiolarien-Systems auf Grund von Studien der Challenger-Radiolarien (Jenaische Zeitschr. f. Naturw., Bd. xv., 1881). Since the manuscript of this preliminary communication was completed only a few days before my departure for Ceylon, and since I was unable to correct the proofs myself, several errors have crept into the Prodromus Systematis Radiolarium included in it. These have been corrected in the following more extensive working out of it. Even at that time I had distinguished 630 genera and more than 2000 species; but on the revision of these, which I undertook immediately on my return from India, this number was considerably increased. The total number of forms here described amounts to 739 genera and 4318 species; of these 3508 are new, as against 810 previously described. In spite of this large number, however, and in spite of the astonishing variety of the new and marvellous forms, the riches of the Challenger collection are by no means exhausted. A careful and patient worker who would devote a second decade to the work, would probably increase the number of new forms (especially of the smaller ones) by more than a thousand; but for a really complete examination, the lifetime of one man would not suffice.

The richest source of the Challenger material is the Radiolarian ooze of the central Pacific Ocean (Stations 265 to 274). This remarkable deep-sea mud consists for the greater part of well-preserved siliceous shells of Polycystina (Spumellaria and Nassellaria). Not less important, however, especially for the study of the Acantharia and PhÆodaria, are the wonderful preparations stained with carmine and mounted in Canada balsam on the spot by Dr. John Murray. One such preparation (e.g., from Station 271) often contains twenty or thirty, sometimes even fifty new species. In many of these preparations the individual parts of the unicellular organism are so well preserved that they show clearly the characteristic peculiarities of the legions and orders. Since the material for these preparations was taken with the tow-net, not only from the surface of the sea but also from different bathymetrical zones, it furnishes valuable conclusions regarding the chorology, as well as the physiology and morphology of the group. For many new discoveries I am indebted to the study of such preparations, of which I have examined about a thousand from 168 different Stations (compare § 240). In addition to these about 100 bottles were handed to me, containing partly bottom-deposits, partly tow-net gatherings.

Sir Wyville Thomson, who directed the investigations of the Challenger with so much devotion, and only partly saw its results, has laid me under a deep debt of obligation; not less is this the case, however, with his successor, Dr. John Murray. I am especially indebted to both gentlemen for the freedom they have allowed me in the carrying out of my work, and especially for the permission to include a description of all known Radiolaria in the Challenger Report, which has thus become a second edition many times enlarged of my Monograph published in 1862. Since all previous literature of the subject has been consulted and critically revised, it is hoped that this Report will form a useful foundation for future investigations. All names of sufficiently described Radiolaria published during the first half century of our knowledge of the class (from 1834 to 1884), are inserted in alphabetical order in the index at the end of this work.

In addition to the treasures of the Challenger, my own collection of Radiolaria has yielded many new forms whose description is here included. On my journeys to the Mediterranean (an account of which is given in the introduction to my Monograph of the MedusÆ), I have given special attention to these delicate microscopic organisms for more than thirty years. Besides the various points on the Mediterranean, the Atlantic Ocean at the Canaries (in the winter of 1866-67) yielded many interesting new forms; whilst my voyage across the Indian Ocean, from Aden to Bombay, in November 1881, thence to Ceylon and back by Socotra in March 1882, was still more productive. In particular, some extended excursions which I had the opportunity of making from Belligemma and Matura (at the southern extremity of Ceylon) gave me an insight into the rich treasures of the Indian Ocean.

Most important, however, as regards the knowledge of the Indian Radiolaria, are the collections which Captain Heinrich Rabbe of Bremen has so beautifully preserved during his many voyages through that region. In the neighbourhood of Madagascar and the Cocos Islands more especially, and also in the Sunda Archipelago, he met with large swarms of Radiolaria, among which were many new and remarkable forms. These were of special value for completing the chorology, and the more so since the course of the Challenger in the Indian Ocean lay very far to the southwards. I will therefore take this opportunity of repeating my best thanks to Captain Rabbe for the friendly donation of his valuable collection.

The Radiolarian fauna of the North Atlantic Ocean, which was previously but little known and only slightly increased by the investigations of the Challenger, received a valuable increase from the interesting collections made by Dr. John Murray on various expeditions to the FÆrÖe Islands (on the "Knight Errant" in 1880 and on the "Triton" in 1882). A large number of new Radiolaria were captured in the FÆrÖe Channel, partly at the surface of the Gulf Stream, partly at various depths, and the proof was thus furnished that at certain points in the North Atlantic Ocean Radiolaria are very richly developed. I am further indebted to Dr. John Murray for the free use of this important material as well as for much other assistance in the carrying out of my work. Another rich source of Radiolaria I found in the alimentary canal of pelagic animals from all seas. MedusÆ, SiphonophorÆ, SalpÆ, Pteropoda, Heteropoda, Crustacea, &c., which live partly at the surface of the sea and partly at various depths, and swallow large masses of Radiolaria, often contain numbers of their shells well-preserved in their intestine. The alimentary canal of Fishes and Cephalopods too, which live upon these pelagic animal frequently contains considerable quantities of siliceous shells; and another newly discovered source has been found in the coprolites of the Jurassic period, which consist largely of Radiolarian skeletons.

In the investigation of this complicated system of organisms, I have endeavoured on the one hand to give accurately the forms and dimensions of the species observed, and on the other hand to present a survey of the relationships of the different genera and families; and in this I have striven especially to combine the phylogenetic aims of the natural system with the essentially artificial divisions of a practical classification. Being, however, a conscientious supporter of the theory of descent, I can of course lay no stress upon the value of the categories, which are here distinguished as Legions, Orders, Families, Genera, &c. All these artificial systematic grades I regard as of merely relative value; and from the same cause I attach no importance to the distinction of all the species here described; many of them are probably only developmental stages, and like my predecessors I have determined their boundaries on subjective grounds. In the systematic working out of so much material one always runs the risk of doing either too much or too little in the way of creating species; but in the light of the theory of descent this danger is of no consequence.

The figures of new species of Radiolaria (about 1600 in number) which appear in the atlas of one hundred and forty plates accompanying this Report, were nearly all drawn with the camera lucida, partly by Mr. Adolph Giltsch and partly by myself. The names of the genera which appear at the bottom of the plates have in many cases been changed since they were printed off, as may be seen from the explanations which accompany them. Had it been possible to complete the examination of the material before the plates were commenced this might have been avoided, and in many cases a better selection of figures might have been made. All the drawings have been made upon the stone by the practised hand of Mr. Adolph Giltsch, in his usual masterly manner, and his lithographic work, which has lasted fully ten years, is the more valuable since he has himself microscopically studied the greater part of the species figured. The fact that the atlas presents so full a picture of the marvellous wealth of form of the Radiolaria is especially due to his lively interest in the work, to his unwearying care, and to his morphological acuteness. May it be the means of inducing many naturalists to study more deeply this inexhaustible kingdom of microscopic life, whose endless variety of wonderful forms justifies the saying—Natura in minimis maxima.

CONTENTS.

FIRST PART.
GENERAL INTRODUCTION— PAGE
I. Anatomical Section (§§ 1-140), i
Chapter I. The Unicellular Organism, i
" II. The Central Capsule, xxiv
" III. The Extracapsulum, li
" IV. The Skeleton, lxviii
II. Biogenetical Section (§§ 141-200), xciii
Chapter V. Ontogeny (Individual Development), xciii
" VI. Phylogeny (Genealogical Development), ci
III. Physiological Section (§§ 201-225), cxxviii
Chapter VII. Vegetative Functions, cxxviii
" VIII. Animal Functions, cxl
IV. Chorological Section (§§ 226-250), cxlvi
Chapter IX. Geographical Distribution, cxlvi
" X. Geological Distribution, clxiv
V. Bibliographical Section (§§ 251-254), clxxvi
SYSTEMATIC PART, 1
I. Subclass PORULOSA, 6
Legion I. SPUMELLARIA vel PERIPYLEA, 6
Order 1. Colloidea, 10
" 2. Beloidea, 28
" 3. SphÆroidea, 50
" 4. Prunoidea, 284
" 5. Discoidea, 402
" 6. Larcoidea, 599
Legion II. ACANTHARIA vel ACTIPYLEA, 716
Order 7. Actinelida, 728
" 8. Acanthonida, 740
" 9. SphÆrophracta, 795
" 10. Prunophracta, 859

GENERAL INTRODUCTION.

ANATOMICAL SECTION.

A SKETCH OF OUR KNOWLEDGE OF THE ORGANISATION OF THE RADIOLARIA IN THE YEAR 1884.

Chapter I.—THE UNICELLULAR ORGANISM.

(§§ 1-50.)

1. Definition of the Radiolaria.—Radiolaria are marine Rhizopoda, whose unicellular body always consists of two main portions, separated by a membrane; an inner Central capsule (with one or more nuclei) and an Extracapsulum (the external calymma, which has no nucleus, and the pseudopodia); the endoplasm of the former and the exoplasm of the latter are connected by openings in the capsule-membrane. The central capsule is partly the general central organ of the Radiolarian cell, partly the special organ of reproduction, since its intracapsular protoplasm, along with the nuclei embedded in it, serves for the formation of flagellate spores. The extracapsulum is partly the general organ for intercourse with the outer world (by means of the pseudopodia), partly the special organ of protection (calymma) and nutrition (sarcomatrix). The majority of Radiolaria develop also a skeleton for support and protection, which presents the utmost variety of form, and is generally composed of silica, sometimes of an organic substance (acanthin). The Radiolarian cell usually leads an isolated existence (Monozoa vel Monocyttaria); only in a small minority (of one legion) are the unicellular organisms united in colonies or coenobia (Polyzoa vel Polycyttaria).

The extent of the Radiolaria, as limited by the above definition, which I have made as compact as possible, differs in several important respects from that allowed to the group by all previous diagnoses. The shortest expression of its scope might perhaps be:—Rhizopoda with central capsule and calymma; for the most important character of the Radiolaria, and that by which they are distinguished from all other Rhizopoda, is the differentiation of the unicellular body into two principal parts of equal importance and their separation by a constant capsule-membrane.

2. The Two Subclasses of the Radiolaria.—The systematic catalogue of the Radiolaria, which forms the second part of this Report, and is brought up to the year 1884, contains 20 orders, 85 families, 739 genera, and 4318 species. The consideration that but a small proportion of the ocean his yet been investigated renders it likely, however, that even this large number does not include the half of the recent species. The great progress which our knowledge of the organisation of the Radiolaria has made, by means of comparative study, renders it possible to arrange this enormous mass of forms in four main divisions or legions, and these are again related in pairs, so that two divisions of the highest rank or subclasses are constituted, the Porulosa (or Holotrypasta) and Osculosa (or Merotrypasta).

The division of the Radiolaria into two subclasses and four legions (or principal orders), I sought to establish in 1883 in a communication on the Orders of the Radiolaria (Sitzb. Jena Gesellsch. Med. u. Naturwiss., February 16, 1883). As a believer in the theory of descent, I regard all the systematic arrangements of specialists as artificial, and all their divisions as subjective abstractions, and hence I shall be guided in the establishment of such groups as subclasses, legions, orders, &c., by purely practical considerations, especially by the desire to give as ready a survey as possible of the complex multitude of forms (compare §§ 154 to 156).

3. Porulosa or Holotrypasta.—The subclass Porulosa or Holotrypasta includes the two legions, Peripylea or Spumellaria, and Actipylea or Acantharia, which agree in the following constant and important characters:—(1) The Central Capsule is primitively a sphere, and retains this homaxon form in the majority of the species. (2) The Membrane of the central capsule is everywhere perforated by very numerous minute pores, but possesses no larger principal aperture (osculum). (3) The Pseudopodia radiate in all directions and in great numbers from the central capsule, passing through its pores. (4) The Equilibrium of the floating unicellular body is in most Porulosa pantostatic (indifferent) or polystatic (plural-stable), since a vertical axis is either absent, or, if present, has its two poles similarly constituted. (5) The Ground-forms of the skeleton are therefore almost always either spherotypic or isopolar-monaxon, very rarely zygotypic. The two legions of the Porulosa are distinguished mainly by the skeleton of the Spumellaria (or Peripylea) being siliceous, never centrogenous, nor composed of acanthin, whilst in the Acantharia (or Actipylea) it is always centrogenous and made up of acanthin; hence in the former the nucleus is always central, in the latter always excentric.

4. Osculosa or Merotrypasta.—The subclass Osculosa or Merotrypasta includes the two legions Monopylea or Nassellaria, and Cannopylea or PhÆodaria, which agree in the following constant and important characters:—(1) The Central Capsule is originally monaxon (ovoid or spheroidal) and retains this ground-form in most of the species. (2) The Membrane of the central capsule possesses a single large principal aperture (osculum) at the basal pole of the vertical main axis. (3) The Pseudopodia radiate from a stream of sarcode which passes out from the central capsule only on one side, namely, through the principal aperture. (4) The Equilibrium of the floating body is monostatic or unistable, since the two poles of the principal axis are always more or less different from each other. (5) The Ground-forms of the skeleton are, therefore, for the most part grammotypic (centraxon) or zygotypic (centroplan), rarely spherotypic. The two legions of the Osculosa are distinguished chiefly by the principal opening (osculum) being closed by a porous plate (porochora with its podoconus) in the Nassellaria (or Monopylea), and by a radiate cover (operculum with its astropyle) in the PhÆodaria (or Cannopylea).

5. The four Legions of Radiolaria.—The four principal groups of Radiolaria, to which we have given the name "legions," are natural units, since the most important peculiarities in the structure of the central capsule are quite constant within the limits of the same legion, and since all the forms in the same legion may be traced without violence to the same phylogenetic stem. The four legions are, however, related to each other, in so far as they all exhibit those characters which distinguish the Radiolaria from other Protista. The two which compose the Porulosa (§ 3) seem somewhat more nearly related to each other than to the two which make up the Osculosa (§ 4). When, however, the attempt is made to bring them all into a phylogenetic relationship, it undoubtedly appears that the Spumellaria (or Peripylea) are the primitive stem, out of which the other three have been developed as independent branches. All three have been derived, probably independently, from the most ancient stem-form of the Spumellaria, the spherical Actissa.

6. Peripylea or Spumellaria.—Those Radiolaria which we call "Peripylea" on account of the constitution of their central capsule, or "Spumellaria" on account of the nature of their skeleton, are separated from the other three legions of the class by the combination of the following constant characters:—(1) The Membrane of the central capsule is single and evenly perforated all over by innumerable fine pore-canals, but without any larger principal opening (osculum). (2) The Nucleus always lies centrally in the Spumellaria monozoa and is serotinous, for it divides only at a later period into the nuclei of the spores; in the Spumellaria polyzoa it is precocious, and divides early into many small nuclei. (3) The Pseudopodia are exceedingly numerous and distributed evenly over the whole surface of the central capsule. (4) The Calymma contains no phÆodium. (5) The Skeleton is seldom wanting, is never centrogenous, and is always siliceous. (6) The Ground-form of the central capsule is originally spherical (often modified); that of the skeleton is also spherical or, in the majority of cases, derived in different ways from the sphere.

7. Actipylea or Acantharia.—These Radiolaria which we call "Actipylea" on account of the constitution of their central capsule, or "Acantharia" from the formation of their skeleton, are separated from the other three legions by the combination of the following constant characters:—(1) The Membrane of the central capsule is single and perforated by numerous fine pore-canals, which are regularly distributed in series or groups, but without a larger principal opening (osculum). (2) The Nucleus is always excentric and generally precocious, since it divides early by a peculiar process of budding into numerous small nuclei. (3) The Pseudopodia are very numerous and distributed regularly in groups (or series united into a network). (4) The Calymma contains no phÆodium. (5) The Skeleton is generally present, always centrogenous, and composed of acanthin. (6) The Ground-form of the central capsule is originally spherical (often modified), that of the skeleton polyaxon (often modified).

8. Monopylea or Nassellaria.—Those Radiolaria which we call "Monopylea" from the formation of their central capsule, or "Nassellaria" from the nature of their skeleton, are distinguished from the other three legions of the class by the combination of the following constant characters:—(1) The Membrane of the central capsule is single, and has only one large principal opening (osculum) at the basal pole of the vertical main axis; this osculum is closed by a perforated lid (porochora or operculum porosum) from which there arises within the central capsule a peculiar cone of threads or pseudopodia (podoconus). (2) The Nucleus is usually excentric and is always serotinous, since it only divides at a comparatively late period into spore-nuclei. (3) The Pseudopodia are not very numerous and arise by division of a single stem or bundle of threads of sarcode, which issues from the porochora. (4) The Calymma contains no phÆodium. (5) The Skeleton (very rarely absent) is never centrogenous, but always extracapsular and siliceous. (6) The Ground-form of the central capsule is always monaxon (with a vertical allopolar main axis), originally ovoid, often modified; that of the skeleton is also generally monaxon, often modified (triradial or bilateral).

9. Cannopylea or PhÆodaria.—Those Radiolaria which we call "Cannopylea" from the constitution of their central capsule, or "PhÆodaria" on account of their peculiar phÆodium, are distinguished from the other three legions by the combination of the following characters:—(1) The Membrane of the central capsule is double, consisting of a strong outer and delicate inner capsule, and has only one principal opening (osculum) at the basal pole of the vertical main axis; this osculum is closed by a radiate cover (astropyle or operculum radiatum), from the centre of which arises an external tubular spout (proboscis). Occasionally a few small accessory openings (parapylÆ) are present besides the principal opening. (2) The Nucleus lies centrally or subcentrally in the capsule (in the vertical main axis), and is serotinous, inasmuch as it only divides at a late period into spore-nuclei. (3) The Pseudopodia are usually very numerous and arise from a thick sarcomatrix, formed by the spreading out of a thick stem of sarcode, which issues from the astropyle. (4) The Calymma always contains a phÆodium or peculiar voluminous excentric mass of pigment. (5) The Skeleton (very rarely absent) is never centrogenous, always extracapsular and formed of a silicate of carbon. (6) The Ground-form of the central capsule is always monaxon (with a vertical allopolar main axis) and generally spheroidal; that of the skeleton is very varied.

10. Synopsis of the Subclasses and Legions:—

First Subclass. Second Subclass.

Porulosa vel Holotrypasta.

Central capsule originally spherical, without osculum or principal opening, with innumerable fine pores.

Osculosa vel Merotrypasta.

Central capsule originally monaxon, with an osculum at the basal pole of the vertical main axis.
Legion I.
Spumellaria.
(Peripylea).		 Legion II.
Acantharia.
(Actipylea).		 Legion III.
Nassellaria.
(Monopylea).		 Legion IV.
PhÆodaria.
(Cannopylea).
Central capsule originally spherical, homaxon. Central capsule originally spherical, homaxon. Central capsule originally ovoid, monaxon. Central capsule always spheroidal, monaxon.
Capsule-membrane single,
pores innumerable, distributed all over.		 Capsule-membrane single,
pores numerous, regularly distributed.		 Capsule-membrane single,
a porous area (porochora) at the oral pole of the main axis.		 Capsule-membrane always double,
an astropyle (with radiate operculum) at the oral pole of the main axis.
Nucleus central, originally spherical (usually dividing late). Nucleus excentric, (usually dividing early). Nucleus excentric, near the aboral pole (dividing late). Nucleus always spheroidal, in the main axis (dividing late).
Skeleton absent or siliceous, never centrogenous. Skeleton always of acanthin, always centrogenous. Skeleton siliceous, usually monaxon, extracapsular. Skeleton of a silicate, always extracapsular.
Calymma always without phÆodium. Calymma always without phÆodium. Calymma always without phÆodium. Calymma always with phÆodium.
First Subclass.

Porulosa vel Holotrypasta.

Central capsule originally spherical, without osculum or principal opening, with innumerable fine pores.
Legion I.
Spumellaria.
(Peripylea).		 Legion II.
Acantharia.
(Actipylea).
Central capsule originally spherical, homaxon. Central capsule originally spherical, homaxon.
Capsule-membrane single, pores innumerable, distributed all over. Capsule-membrane single, pores numerous, regularly distributed.
Nucleus central, originally spherical (usually dividing late). Nucleus excentric, (usually dividing early).
Skeleton absent or siliceous, never centrogenous. Skeleton always of acanthin, always centrogenous.
Calymma always without phÆodium. Calymma always without phÆodium.
Second Subclass.

Osculosa vel Merotrypasta.

Central capsule originally monaxon, with an osculum at the basal pole of the vertical main axis.
Legion III.
Nassellaria.
(Monopylea).		 Legion IV.
PhÆodaria.
(Cannopylea).
Central capsule originally ovoid, monaxon. Central capsule always spheroidal, monaxon.
Capsule-membrane single, a porous area (porochora) at the oral pole of the main axis. Capsule-membrane always double, an astropyle (with radiate operculum) at the oral pole of the main axis.
Nucleus excentric, near the aboral pole (dividing late). Nucleus always spheroidal, in the main axis (dividing late).
Skeleton siliceous, usually monaxon, extracapsular. Skeleton of a silicate, always extracapsular.
Calymma always without phÆodium. Calymma always with phÆodium.

11. Individuality of the Radiolaria.—Like other Protozoa the Radiolaria are unicellular organisms, the whole fully developed organisation of which falls under the category of a single cell, both morphologically and physiologically. Since this view is based upon the composition of the individual body out of two different morphological elements, nucleus and protoplasm, it is at once justified in the case of the majority of Radiolaria, in which the plasmatic body encloses only a single nucleus (the so-called "Binnen-BlÄschen"); such is the case in all the Spumellaria monozoa, Nassellaria and PhÆodaria. This aspect of the case might appear doubtful in those Radiolaria in which the simple primary cell-nucleus divides early into numerous small secondary nuclei, as is the case in the Spumellaria polyzoa and most Acantharia. Strictly speaking, the multinucleate central capsule should in such cases be regarded as a syncytium; but since the individual unity of the unicellular organism is as clearly defined in these precocious multinuclear Radiolaria as in the ordinary serotinous forms, the former must be considered unicellular Rhizopods just as are the latter. This mode of regarding the case is the more necessary, inasmuch as the early division of the nucleus has no further influence upon the organisation. Just as in many other classes of the Protista there are monozootic (solitary) and polyzootic (social) forms, so also in the Radiolaria there are in addition to the ordinary monozootic or monobious forms certain families in which colonies or coenobia are formed by the association of individuals; this distinction may be expressed by the terms "Monocyttaria" and "Polycyttaria."

The unicellular nature of the Radiolaria was first established by Richard Hertwig in 1879 (L. N. 33),[1] and brought into conformity with our present histiological knowledge and the new reform of the cell-theory. Huxley, however, who was in 1851 the first to examine living Radiolaria accurately, declared Thalassicolla nucleata to be a unicellular Protozoon, and the individual central capsules of SphÆrozoum punctatum to be cells, but, owing to the then condition of the cell-theory, he was unable to give a conclusive demonstration of this view. Later, when Johannes MÜller in 1858 and myself in 1862 recognised the peculiar "yellow cells" which occur in large numbers in many Radiolaria as true nucleated cells, it appeared impossible any longer to maintain the unicellular nature of the Radiolaria; also the great complication which I showed to exist in the structure of Thalassicolla appeared to contradict it. Only after Cienkowski (1871) and Brandt (1881) had shown that the "yellow cells" do not belong to the Radiolarian organism, but are symbiotic unicellular algÆ, was it possible to revive and demonstrate anew the unicellular nature of the Radiolaria.

12. Morphological Individuality.—From the morphological standpoint the individuality of the unicellular elementary organism is obvious in the ordinary solitary Radiolaria (Monobia), and is to be so regarded that the whole body with all its constituent parts, and not merely the central capsule, is to be regarded as a cell. Naturally the xanthellÆ or yellow cells (§§ 76, 90), which as independent algÆ live in symbiosis with many Radiolaria, must be excluded. The unicellular organisation of the Radiolaria is further to be distinguished from that of the other Protista, inasmuch as an internal membrane (capsule-membrane) separates the central (medullary) from the peripheral (cortical) portion. In the coenobia of the social Radiolaria (or Polycyttaria), the morphological individuality persists only as regards the medullary portions of the aggregated cells (the individual central capsules), while the cortical portions fuse completely to form a common extracapsulum. Hence in these Spumellaria polyzoa two different stages of morphological individuality must be distinguished, the Cell as a Morphon of the first stage, and the Coenobium as a Morphon of the second stage.

13. Physiological Individuality.—From the physiological standpoint also the individuality of the unicellular organism is immediately obvious in the case of the ordinary solitary Radiolaria (Monobia); as in other Protista it fulfils all the functions of life by itself alone. This physiological individuality of the monobious Radiolarian cell is furthermore not influenced by the xanthellÆ, which live as independent algÆ in symbiosis with many Radiolaria; even though these often by the production of starch assist in the nourishment of the Radiolaria, yet they are by no means indispensable to them. On the other hand, the physiological individuality offers more complicated relations in the social Radiolaria (Polycyttaria) which live united in colonies or coenobia. Here the actual Bion (or the fully developed physiological individual) is not represented by the individual cells, but by the whole multicellular coenobium, which in each species has a definite form and size. In these coenobia, which are usually spherical or cylindrical jelly-like masses, several millimeters in diameter, numerous cells are so intimately united that only their medullary portions (the central capsule with the endoplasm) remain independent; the cortical portions (calymma and exoplasm) on the contrary uniting into a common extracapsulum. This discharges, as a whole, the functions of locomotion, sensation, and inception of nutriment, while the separate central capsules act in the main only as reproductive organs (forming spores) and partly also as the central organs of metastasis (digestion). Each coenobium may also be regarded as a polycyttarium, i.e., a "multicellular Radiolarian," whose numerous central capsules represent so many sporangia or spore-capsules.

On this head compare the section in my monograph of 1862 (L. N. 16), entitled Die Organisation der Radiolarien-Colonien; Polyzoen oder Polycyttarien? (pp. 116 to 126); and also R. Hertwig, Zur Histologie der Radiolarien, 1876 (L. N. 26, p. 23).

The colonial Radiolaria were described as early as the year 1834 by Meyen, the first investigator of the class, under the name SphÆrozoum, and, as Palmellaria, compared with the gelatinous colonies of the NostochineÆ. The first accurate observations upon their structure were, however, made in 1851 by Huxley, who described examples of all three families under the name Thalassicolla punctata. More extended, however, were the investigations of Johannes MÜller, who in his fundamental work (1858) divided the whole class Radiolaria into Solitaria and Polyzoa. The Radiolaria solitaria he divided into Thalassicolla, Polycystina and Acanthometra, the Radiolaria polyzoa into SphÆrozoa (without a shell) and CollosphÆra (with a shell). The most accurate delineation of the Polycyttaria was given by Hertwig in his beautiful memoir, Zur Histologie der Radiolarien (1876). Quite recently, however (1886), since the completion of my manuscript upon the Challenger Radiolaria, a very complete Monograph of the Polycyttaria has appeared by Karl Brandt, Die colonie-bildenden Radiolarien (SphÆrozoen) des Golfes von Neapel und der angrenzenden Meeres-Abschnitte (276 pp., 8 pls., Berlin). It contains in particular most valuable contributions to the physiology and histology.

15. The Central Capsule and Extracapsulum.—The special peculiarity of the unicellular Radiolarian organism, by which it is clearly distinguished from all other Rhizopoda (and indeed from most other Protista), is its differentiation into two separate chief constituents, the central capsule and extracapsulum, and the formation of a special membrane which separates them. This, the capsule-membrane, is not to be compared with an ordinary cell-membrane, as an external layer, but rather to be regarded as an internal differentiated product. The extracapsulum or external (cortical) portion of the body is in most Radiolaria more voluminous than the central capsule or inner (medullary) portion. The exoplasm of the former (the cortical or extracapsular protoplasm) is emphatically different from the endoplasm of the latter (the medullary or intracapsular protoplasm). Besides the most important vital processes are distributed by division of labour so completely between them that they appear most distinctly co-ordinated. The central capsule is on the one hand the general central organ of the "cell-soul" for the discharge of its sensory and motor functions (comparable to a ganglion-cell), on the other hand the special organ of reproduction (sporangium). The extracapsulum, also, is not less significant, since on the one hand its calymma acts as a protecting envelope to the central capsule, as a support to the pseudopodia, and a foundation for the skeleton or a matrix for the development of the shell, and on the other hand its pseudopodia are of the utmost importance as peripheral organs of movement and sensation as well as of nutrition and respiration. The central capsule and the extracapsulum are therefore to be regarded both morphologically and physiologically as the two characteristic co-ordinated principal parts of the unicellular Radiolarian organism.

In most of the more modern delineations of the Radiolaria the central capsule is regarded as the "cell proper" and its membrane as the "cell-wall." The following facts are opposed to the correctness of this interpretation:—1. In most Radiolaria the exoplasm is clearly different from the endoplasm, and the former is more voluminous than the latter. 2. In all Radiolaria the division of labour is so carried out between the central capsule and the extracapsulum, that the physiological significance and independence of both principal parts of the cell is almost equally great. 3. It is only in the Acantharia that the formation of the skeleton takes place within the central capsule; in all the other three legions it is quite independent of it.

16. The Malacoma and Skeleton.—Whilst the division of the unicellular organism into central capsule and extracapsulum is undoubtedly the most important character of the Radiolarian organism, the development of a skeleton of peculiar and most varied form is of very striking significance. This skeleton is always a secondary product of the cell, but is always anatomically so independent, and so clearly marked off from the soft parts or malacoma, that it seems advisable to regard both separately in a general morphological survey. The skeleton stands in a different relation to each of the two principal constituents of the malacoma. Only in the Acantharia is it centrogenous and developed from the central capsule outwards. In the other three legions the skeleton never arises in the centre of the capsule; in the Nassellaria and PhÆodaria it is always extracapsular; in the Spumellaria it is also outside the central capsule originally, but afterwards becomes often surrounded by it, and finally lies in most cases partly within and partly without the central capsule. The chemical basis of the skeleton in the Acantharia is the curious acanthin (an organic substance allied to chitin), in the PhÆodaria a silicate of carbon, and in the Nassellaria and Spumellaria silica.

17. Ground-Forms of the Radiolaria (Promorphology).—The ground-forms of the Radiolaria exhibit a greater variety than those of any other class in the organic world, greater indeed than is to be found in all the remaining groups together. For every conceivable ground-form which can be defined in the system of promorphology is actually present in the Radiolaria; their skeleton exhibits, as it were, in material existence, certain geometrical ground-forms which are found in no other organisms. The cause of this unexampled richness in different forms lies chiefly in the static relations of the Radiolaria, which swim freely in the sea, partly also in the peculiar plasticity of their protoplasm and the material of their skeletons.

Regarding the general system of ground-forms compare my Generelle Morphologie (1866, Bd. i. pp. 375-552; Bd. iv., Allgemeine Grundformenlehre). The ground-forms there proposed and systematically defined have, however, found but little acceptance (chiefly, no doubt, owing to the difficult and complicated nomenclature); but having now, twenty years after their publication, anew carefully revised and critically studied them, I can find no sufficient reason for abandoning the principles there adopted. On the contrary the study of the Challenger Radiolaria during the last ten years, with its incomparable wealth of forms, has only confirmed the accuracy of my system of ground-forms. The customary treatment of these in zoological and botanical handbooks (such as those of Claus and Sachs) is quite insufficient.

18. The Principal Groups of Geometrical Ground-Forms.—The great variety of the geometrical ground-forms which are actually realised in the variously shaped bodies of the Radiolaria, renders it desirable to classify these in as small a number as possible of principal groups and a larger number of subdivisions. As extensive principal groups four at least must be distinguished; the Centrostigma or SphÆrotypic, the Centraxonia or Grammotypic, the Centroplana or Zygotypic, and the Acentrica or Atypic. The natural centre of the body, about which all its parts are regularly arranged, is in the first group a point (stigma), in the second a straight line (principal axis), in the third a plane (sagittal plane), in the fourth a centre is of course wanting.

19. The Centrostigma or SphÆrotypic Ground-Forms.—The first group of geometrical ground-forms, here distinguished as sphÆrotypic or the centrostigma, is undoubtedly the most important among the Radiolaria, inasmuch as if these be considered monophyletic, it must be the original one from which all the other ground-forms have been derived. The common character of all these sphÆrotypic ground-forms is that their natural centre is a point (stigma); thus there is no single principal axis (or protaxon) such as is characteristic of the two following groups. The sphÆrotypic ground-forms are subdivided into two important smaller groups, the spheres (Homaxonia) and the endospherical polyhedra (Polyaxonia). The spherical ground-forms, fully developed in the central capsule and calymma of Actissa and the SphÆroidea as well as in many Acantharia, present no different axes; all possible axes passing through the centre of the body are equal (Homaxonia). In the endospherical polyhedra, on the contrary, numerous axes (three at least) may be distinguished, which are precisely equal to each other and different from all the remaining axes (Polyaxonia). If the extremities of these axes, or the poles, which are all equidistant from the common centre, be united by straight lines, a polyhedral figure is produced whose angles all lie in the surface of the sphere. According as the poles of the axes are at equal, subequal, or at different distances from each other, we may divide the endospherical polyhedra into regular, subregular and irregular. (See Gener. Morphol., Bd. i. pp. 404-416.)

20. The Centraxonia or Grammotypic Ground-Forms.—The second principal group of organic ground-forms, here called grammotypic or centraxonia, is characterised by the fact that a straight line (gramma) or a single principal axis (protaxon) forms the natural centre of the body. This important and extensive group is divided into two subgroups, those with one axis (Monaxonia) and those with crossed axes (Stauraxonia); in the latter different secondary transverse or cross-axes may be distinguished, but not in the former. In the Monaxonia, therefore, every transverse section of the body perpendicular to the principal axis is a circle, in the Stauraxonia, on the contrary, a polygon. The Monaxonia are further subdivided into two groups, in one of which the two poles of the principal axis are equal and similar (Isopolar), in the other of which they are different (Allopolar); in the former the two halves of the body, which are separated by the equatorial plane (or the largest transverse plane, perpendicular to the principal axis), are equal, in the latter unequal. Among the isopolar uniaxial ground-forms (Monaxonia isopola) may be mentioned the ellipsoidal, spheroidal, lenticular, &c.; to the allopolar uniaxial forms (Monaxonia allopola) belong the conical, hemispherical, ovoid, &c. In the same way the pyramidal ground-forms with crossed axes are divisible into two groups, according as the two poles of the principal axis are equal or not. The ground-form of the former is the double pyramid, that of the latter the single pyramid. Both the double and the single pyramids may again be subdivided, each into two important lesser groups, the regular and the amphithect. In the first division the equatorial plane of the double and the basal plane of the single pyramid is a regular polygon (square, &c.), whilst in the other division it is an elongated or amphithect polygon (rhombus, &c.); the crossed axes are equal in the former, unequal in the latter. (See Gener. Morphol., Bd. i. pp. 416-494.)

21. The Centroplana or Zygotypic Ground-Forms.—The third principal group of ground-forms includes those which are bilaterally symmetrical in the ordinary sense, or zeugitic or zygotypic; the natural centre of their body is a plane. These forms are the only ones in which the distinction between right and left is possible, since their body is divided by the median plane (planum sagittale) into two symmetrical halves (right and left). In all these zeugites the position of every part is determined by three axes perpendicular to each other, and of these three dimensive axes two are allopolar, one is isopolar. The two unlike poles of the principal (or longitudinal) axis are the oral and aboral, the two unlike poles of the sagittal (or vertical) axis are the dorsal and ventral; the two similar poles of the frontal (or transverse) axis, however, are the right and left. This important group of zeugitic or bilateral forms may also be divided into two clearly distinct lesser groups, the Amphipleura and the Zygopleura. In the Amphipleura (or bilaterally radial ground-forms) the "radial two-sided" body is produced by modification of a regular pyramid (as Spatangus from Echinus), and hence is composed of several (not less than three) antimeres. In the Zygopleura (or bilaterally symmetrical ground-forms) on the other hand, the bodies consist of two antimeres (as in all the higher animals, Vertebrata, Arthropoda, &c.). (See Gener. Morphol., Bd. i. pp. 495-527.)

23. The Subsidiary Groups of Geometrical Ground-Forms.—The four natural principal groups of ground-forms, which have just been defined according to the nature of the centre of their bodies, may be divided again into numerous subsidiary groups, defined by the relations of the constant axes and the two poles of each axis, as well as by the number of the axes and the differentiation of the secondary with respect to the principal axis. The most important of these subsidiary groups into which the principal ones are immediately divided are the following:—(1) The Centrostigma (or sphÆrotypic) are divided into spheres (Homaxonia) and endospherical polyhedra (Polyaxonia). (2) The Centraxonia (or grammotypic) into uniaxial (Monaxonia) and those with crossed axes (Stauraxonia); among the former of these may be distinguished the isopolar (phacotypic) and the allopolar (conotypic); among the latter the double and single pyramids. (3) The Centroplana (or bilaterals) are divided into amphipleura (or bilaterally radial) and zygopleura (or bilaterally symmetrical). (4) The Acentrica (or Anaxonia) or absolutely irregular ground-forms, present no special subdivisions.

For a complete system of the geometrical ground-forms and their relation to promorphological classification, see Gener. Morphol., Bd. i. pp. 555-558.

30. The Regular Tetrahedral Ground-Form.—The ground-form whose geometrical type is the regular tetrahedron, bounded by four equilateral triangles, occurs less frequently in the Radiolaria than the other four regular polyhedra. Among the Spumellaria it is found in the Beloidea, and especially in those members of the ThalassosphÆrida and SphÆrozoida whose spicules bear four equal branches, diverging at equal angles from a common centre. Precisely the same structure is seen also among the Nassellaria in some Plectoidea, as in Tetraplagia among the Plagonida, and Tetraplecta among the Plectanida. The skeleton of both these genera consists of four equal rods, which radiate at equal angles from a common centre, just as do the axes of the regular tetrahedron. The tetrahedral form of these Plectoidea is the more important and interesting since on the one hand it is related to the similar spicular form of the Beloidea, and on the other perhaps furnishes the starting point from which Cortina among the Nassellaria may be derived (Plagoniscus, Plectaniscus). (See Gener. Morphol., Bd. i. p. 415.)

31. The Isopolar-Monaxon or Phacotypic Ground-Form.—The isopolar uniaxial or phacotypic ground-form is characterised by the possession of a vertical main axis with equal poles, whilst no transverse axes are differentiated. All horizontal planes which cut the axis at right angles are circles, and increase in size from the poles towards the equator. The most important ground-forms of this group are the phacoid (the lens or oblate spheroid) and the ellipsoid (or prolate spheroid). Phacoids (or geometrical lenses with blunt margins) are very often presented by the central capsules of the Discoidea and of many Acantharia (Quadrilonchida and Hexalaspida), but the lattice-shells of many Spumellaria and Acantharia exhibit the same form, as also do a few PhÆodaria (e.g., Aulophacus). True geometrical ellipsoids are seen in the central capsules of many Prunoidea among the Spumellaria, and of many Amphilonchida and Belonaspida among the Acantharia. Furthermore, the lattice shells of many species of these groups retain the same essential form, e.g., many Ellipsida, Druppulida, and Spongurida (Pls. 13-17, and 39), as well as most Belonaspida. (See Gener. Morphol., Bd. i. p. 422.)

37. The Amphipleural Ground-Forms.—By the term amphipleural ground-forms are to be understood those usually defined as "bilaterally radial"; their geometrical type is a half amphithect pyramid. The best known examples of this form in the animal kingdom are the bilateral five-rayed Echinoderms (Spatangus, Clypeaster), in the vegetable kingdom the symmetrical five-rayed flowers (Viola, Trifolium). The three dimensive axes have the same relation as in the zygopleura, to be next discussed, and which also resemble them in being divisible only by one plane (the sagittal median plane) into two equal halves. They differ, however, the amphipleural body not being made up of two antimeres, but of at least three pairs of antimeres (or three parameres), being therefore primitively radial. Hence each of the symmetrical halves of the body contains more than one antimere. Among the Radiolaria this form does not occur in the Spumellaria, Acantharia, or PhÆodaria; it is very common, however, among the Nassellaria; many Cyrtoidea multiradiata and Spyroidea multiradiata show this bilaterally radial ground-form, inasmuch as the body consists of two symmetrical halves, and is also composed of numerous (usually three, six, nine, or more) radial parameres. In the multiradiate Dicyrtida and Tricyrtida the cephalis (the first joint) is usually bilateral, whilst the thorax (the second joint) is multiradial. (See Gener. Morphol., Bd. i. pp. 495-506.)

39. Synopsis of the Geometrical Ground-Forms:—

Principal Groups of
Ground-Forms.		 Subsidiary Groups of
Ground-Forms.		 Geometrical Type. Examples.

I. Centrostigma.

The geometrical centre of the body is a point. Main axis wanting.

 brace

I. Homaxonia.

All axes equal

 brace 1. Sphere, brace Central capsule of the SphÆroidea and of many Acantharia.

II. Polyaxonia.

Endospherical polyhedra. All the angles of the body lie on the surface of a sphere. Numerous isopolar axes.

 brace 2. Endospherical polyhedron, brace Lattice-spheres of the SphÆroidea, SphÆrophracta, and PhÆosphÆria.
3. Icosahedron, Circogonia.
4. Dodecahedron, Circorrhegma.
5. Octahedron, CubosphÆrida, Circoporus.
6. Cube, Centrocubus, Lithocubus, &c.
7. Tetrahedron, Tetraplagia, Tetraplecta, &c.

II. Centraxonia.

The geometrical centre of the body is a straight line (the vertical main axis).

Constant transverse axes (perpendicular to the main axis) are wanting in the Monaxonia (which have circular transverse sections); on the contrary they are differentiated in the Stauraxonia (which have polygonal transverse sections).

 brace

III. Monaxonia.

Uniaxial ground-forms or centraxonia without transverse axes. The transverse planes (perpendicular to the main axis) are circles.

 brace

8. Monaxonia isopola.

(Spheroids and ellipsoids; both poles of the main axis similar.)

 brace Central capsule and lattice-shell of of many Discoidea (lenses) and Prunoidea (ellipsoids), Belonaspida, &c.

9. Monaxonia allopola.

(Cone, ovoid and hemisphere; the two poles of the axis dissimilar.)

 brace Central capsule and lattice-shell of many Nassellaria, especially the Cyrtoidea eradiata (Cyrtocalpida, &c.).

IV. Stauraxonia.

Pyramidal ground-forms or centraxonia with transverse axes. The transverse planes (perpendicular to the main axis) are either regular or amphithect polygons.

 brace

10. Dipyramides regulares.

(Quadratic octahedron, or quadrilonchial forms and regular double pyramids.)

 brace Acantharia with twenty radial spines, the four equatorial being equal. Multiradial Discoidea and StaurosphÆrida.

11. Dipyramides amphithectÆ.

(Rhombic octahedron, lentellipsoid, and amphithect double pyramids.)

 brace Acantharia with twenty radial spines, whose four equatorial spines are unequal but paired. Many Larcoidea.

12. Pyramides regulares.

(Regular pyramids.)

 brace Many Nassellaria (triradial and multiradial). Medusettida and Tuscarorida.

13. Pyramides amphithectÆ.

(Rhombic pyramids.)

 brace PhÆoconchia. Bipedal Spyroidea and Stephoidea.

III. Centroplana.

The geometrical centre of the body is a plane (the sagittal plane).

 brace

V. Bilateralia (or Zeugita).

Bilateral forms in the general sense, with right and left halves.

 brace

14. Amphipleura

(Bilaterally radial ground-form.)

 brace Many Cyrtoidea and Spyroidea multiradiata.

15. Zygopleura.

(Bilaterally symmetrical ground-form.)

 brace Most Nassellaria (primitively at least), many Challengerida.

IV. Acentra.

There is no geometrical centre.

 brace

VI. Anaxonia.

No definite axes can be determined.

 brace

16. Irregularia.

(Absolutely irregular ground-forms.)

 brace Collodastrum, CollosphÆra, Phorticida, Soreumida.
Principal Groups of Ground-Forms.
Subsidiary Groups of Ground-Forms.
Geometrical Type.
Examples.

I. Centrostigma.

The geometrical centre of the body is a point. Main axis wanting.

I. Homaxonia.

All axes equal.
1. Sphere,
  Central capsule of the SphÆroidea and of many Acantharia.

II. Polyaxonia.

Endospherical polyhedra. All the angles of the body lie on the surface of a sphere. Numerous isopolar axes.
2. Endospherical polyhedron,
Lattice-spheres of the SphÆroidea, SphÆrophracta, and PhÆosphÆria.
3. Icosahedron,
Circogonia.
4. Dodecahedron,
Circorrhegma.
5. Octahedron,
CubosphÆrida, Circoporus.
6. Cube,
Centrocubus, Lithocubus, &c.
7. Tetrahedron,
Tetraplagia, Tetraplecta, &c.

II. Centraxonia.

The geometrical centre of the body is a straight line (the vertical main axis).

Constant transverse axes (perpendicular to the main axis) are wanting in the Monaxonia (which have circular transverse sections); on the contrary they are differentiated in the Stauraxonia (which have polygonal transverse sections).

III. Monaxonia.

Uniaxial ground-forms or centraxonia without transverse axes. The transverse planes (perpendicular to the main axis) are circles.

8. Monaxonia isopola.

(Spheroids and ellipsoids; both poles of the main axis similar.)
Central capsule and lattice-shell of of many Discoidea (lenses) and Prunoidea (ellipsoids), Belonaspida, &c.

9. Monaxonia allopola.

(Cone, ovoid and hemisphere; the two poles of the axis dissimilar.)
Central capsule and lattice-shell of many Nassellaria, especially the Cyrtoidea eradiata (Cyrtocalpida, &c.).

IV. Stauraxonia.

Pyramidal ground-forms or centraxonia with transverse axes. The transverse planes (perpendicular to the main axis) are either regular or amphithect polygons.

10. Dipyramides regulares.

(Quadratic octahedron, or quadrilonchial forms and regular double pyramids.)
Acantharia with twenty radial spines, the four equatorial being equal. Multiradial Discoidea and StaurosphÆrida.

11. Dipyramides amphithectÆ.

(Rhombic octahedron, lentellipsoid, and amphithect double pyramids.)
Acantharia with twenty radial spines, whose four equatorial spines are unequal but paired. Many Larcoidea.

12. Pyramides regulares.

(Regular pyramids.)
Many Nassellaria (triradial and multiradial). Medusettida and Tuscarorida.

13. Pyramides amphithectÆ.

(Rhombic pyramids.)
PhÆoconchia. Bipedal Spyroidea and Stephoidea.

III. Centroplana.

The geometrical centre of the body is a plane (the sagittal plane).

Constant transverse axes (perpendicular to the main axis) are wanting in the Monaxonia (which have circular transverse sections); on the contrary they are differentiated in the Stauraxonia (which have polygonal transverse sections).

V. Bilateralia (or Zeugita).

Bilateral forms in the general sense, with right and left halves.

14. Amphipleura

(Bilaterally radial ground-form.)
Many Cyrtoidea and Spyroidea multiradiata.

15. Zygopleura.

(Bilaterally symmetrical ground-form.)
Most Nassellaria (primitively at least), many Challengerida.

IV. Acentra.

There is no geometrical centre.

VI. Anaxonia.

No definite axes can be determined.

16. Irregularia.

(Absolutely irregular ground-forms.)
Collodastrum, CollosphÆra, Phorticida, Soreumida.

40. Mechanical Causes of the Geometrical Ground-Forms.—The great variety of ground-forms exhibited by the Radiolaria is of special interest, since in most instances their causes admit of recognition, and since they are so intimately related to each other that even in the remaining cases the assumption that they have arisen by purely mechanical causÆ efficientes seems justified. In this respect the first rank is taken by statical conditions, especially the indifferent or stable equilibrium of the whole organism, which floats freely in the water. With regard to these fundamental statical relations, three principal groups of ground-forms may be distinguished, pantostatic, polystatic, and monostatic.

41. Pantostatic Ground-Forms.—By pantostatic or indifferently stable ground-forms are meant those in which the centre of gravity coincides with the centre of the body, so that they are in equilibrium in any given position. Strictly speaking, the only form which possesses perfectly indifferent equilibrium is the sphere, that being the only truly homaxon and perfectly regular form. Nevertheless, in a somewhat wider sense many Polyaxonia, especially the endospherical polyhedra with very numerous sides, may be included in this category. Such indifferently stable bodies are found among the Spumellaria in many Collodaria and SphÆroidea, as well as in the Astrolophida among the Acantharia. On the contrary they are entirely wanting among the Nassellaria and PhÆodaria, since their central capsule constantly presents a main axis with a differentiated basal pole, and determines the position of stable equilibrium.

42. Polystatic Ground-Forms.—Those ground forms are defined as polystatic or multistable in which the body is in equilibrium in several different positions (though not in an infinite number). The number of these positions is usually twice as many as that of the constant equal isopolar axes exhibited by the form. Hence the regular polyhedra have as many positions of equilibrium as they have angles or sides, the icosahedron twenty, dodecahedron twelve, octahedron eight, cube six, tetrahedron four. The isopolar monaxon ground-forms (lens, ellipsoid, cylinder) and the diplopyramidal ground forms (quadrilonchial and lentelliptical) have two positions of stable equilibrium, since the two poles of the vertical axis are equal and similar and the body is divided into equal halves by the equatorial plane. This is the case in many Spumellaria (especially Discoidea, Prunoidea, and Larcoidea), as well as in the great majority of Acantharia. Perhaps the same holds good also in certain Nassellaria (e.g., isopolar Tympanida) and PhÆodaria (e.g., isopolar PhÆosphÆria), though here unistable equilibrium appears to be necessitated by the constant main axis of the central capsule and the differentiated basal pole of the main axis.

43. Monostatic Ground-Forms.—Those ground-forms are classed as monostatic or unistable in which the body is in equilibrium only in one position, since the centre of gravity of the body lies in a constant vertical axis below its centre. This fixed position is only rarely and exceptionally found among the Spumellaria (e.g., in Xiphostylus, SphÆrostylus, Lithomespilus, Lithapium) and among the Acantharia (e.g., in Zygostaurus and Amphibelone). On the contrary it is quite usual among the Nassellaria and PhÆodaria (with but few exceptions); for here a vertical main axis, with a differentiated basal pole, is determined even by the formation of the central capsule, and usually also by the corresponding structure of the skeleton. Among the Nassellaria this basal pole, with the porochora of the central capsule, appears always to be the lower; as also in most PhÆogromia among the PhÆodaria. In the peculiar bivalved PhÆoconchia, on the other hand, the basal pole with the cannopyle is directed upwards; as also in the Challengerida and Tuscarorida. The PhÆosphÆria and PhÆocystina are probably to a large extent polystatic. In general unistable equilibrium may be assumed in the following categories of ground-forms:—(1) Allopolar monaxon (conical and ovoid); (2) pyramidal (regular and amphithect); (3) Centroplana (amphipleura and zygopleura); (4) Anaxonia.

44. Principal Axes.—From the foregoing consideration of the statical conditions and their direct causal connection with the geometrical ground-forms of the Radiolaria, the great mechanical significance of the differentiation of definite axes in these unicellular free-swimming organisms will be manifest. The most important of these is the primary main axis (axis principalis, or protaxon), which in all cases has a vertical direction. It is wanting in the Centrostigma (spheres and endospherical polyhedra), and in the Anaxonia (acentra). It is isopolar in the phacotypic forms (Monaxonia isopola), and in the double pyramids (Stauraxonia isopola). It is allopolar in all monastatic ground-forms, in the conotypic forms (Monaxonia allopola), pyramids (Stauraxonia allopola), and the Centroplana (or bilateral forms).

45. Secondary or Transverse Axes.—In contrast to the vertical main axis all the other constant axes differentiated in the body may be called "secondary axes," or "transverse axes," since they cross the former at definite points. All ground-forms whose vertical axis is crossed by a fixed number of such axes at definite angles may be called "Stauraxonia." They are divided into two groups, double pyramids and single pyramids; in the former the two poles of the main axis (or the two halves of the body separated by the equatorial plane) are similar (Stauraxonia homopola), in the latter dissimilar (Stauraxonia heteropola). If all the secondary axes be equal, the stauraxon ground-form is regularly radial. If some of them be unequal they are arranged in certain relations towards two primary transverse axes, perpendicular to each other, to which all the other secondary axes are subsidiary; the ground-forms are then either amphithect or bilateral. The two primary transverse axes, which may also be designated "ideal transverse axes" (euthyni), divide the vertical main axis in its centre; one of them is the sagittal, the other the frontal. These three dimensive axes give the factors which accurately determine the ground-form and the dimensions in most Radiolaria; the vertical main axis determines the length (principal axis); one horizontal transverse axis determines the thickness (sagittal axis), and the other the breadth (frontal axis). Those ground-forms in which the transverse axes are isopolar are termed "amphithect," and those in which the one (frontal or lateral) is isopolar and the other (sagittal or dorso-ventral) is allopolar, are termed "bilateral," or better "zeugitic."

47. The Ground-Forms of the Spumellaria.—The Spumellaria, being the oldest and most primitive Radiolaria, have for the most part either indifferent or multistable equilibrium; e.g., all Colloidea and Beloidea which have a spherical central capsule, and also most SphÆroidea. Among these primitive Centrostigma true spheres and endospherical polyhedra are represented in the utmost variety, and the regular polyhedra in particular. By the development of a vertical main axis these Centrostigma have also given rise to very numerous Centraxonia, which are usually isopolar, very rarely allopolar. Sometimes they are Monaxonia (circular in transverse section), sometimes Stauraxonia (polygonal in transverse section). The vertical main axis is longer in the Prunoidea, shorter in the Discoidea than any of the other axes. The Larcoidea are distinguished by their lentelliptical or triaxial ellipsoid form; the three different but isopolar axes corresponding with those of the rhombic octahedron; but even among the SphÆroidea, Prunoidea, and Discoidea, this form is sometimes produced by the differentiation of two different transverse axes at right angles to each other. Whilst these ground-forms (Centraxonia and Centrostigma) occur in the utmost variety among the Spumellaria, the centroplanar (or true bilateral) ground-form is entirely wanting.

48. The Ground-Forms of Acantharia.—In the small family Astrolophida, which contains the most archaic forms of the legion (Actinelius, Astrolophus), the Acantharia show a direct relation to the most primitive Spumellaria (Actissa), and like these have indifferent equilibrium; their central capsule is a sphere, their calymma an endospherical polyhedron, whose angles are indicated by the distal ends of the numerous equal radial spines. In the great majority of Acantharia, however (all Acanthonida and Acanthophracta), twenty radial spines are present, regularly distributed, according to MÜller's icosacanthan law, in five parallel circles, each containing four crossed spines (p. 717). Usually the twenty spines are equal, and the ground-form is the quadratic octahedron, or a regular double pyramid with sixteen sides. But in some groups (the Amphilonchida and Prunophracta) two opposite equatorial spines are much more strongly developed than the other eighteen, and therefore the hydrotomical axis in the equatorial plane is larger than the geotomical axis (p. 719); the isopolar stauraxonian form passes over into the allopolar, and the ground-form becomes the rhombic octahedron or the amphithect double pyramid (compare §§ 33 and 34, and p. 720). The centroplanar ground-form is entirely wanting in the Acantharia.

49. The Ground-Forms of the Nassellaria.—The Nassellaria all possess monostatic ground-forms, inasmuch as by the very structure of their monopylean central capsule a vertical main axis is necessitated, whose basal pole occupies the porochora. The same arrangement is also for the most part clearly recognisable in the corresponding structure of the skeleton, which is generally either centraxon or centroplanar. Among their manifold skeletal forms different larger groups of ground-forms may be recognised according as the vertical allopolar main axis is crossed by differentiated transverse axes or not (Stauraxonia or Monaxonia); the former are either triradial or multiradial. The triradial, with three lateral or terminal radial apophyses, constitute the greater part of the Nassellaria, and have probably been derived originally from the triradial Plectoidea (Triplagia, Triplecta); a more careful examination, however (especially with reference to the structure of the cortinar septum), reveals the fact that the ground-form is not strictly regularly pyramidal (with three equal radii), but amphipleural (with two paired ventral and one unpaired dorsal radius), and that it usually passes over into a distinctly zygopleural form. The same holds true of the multiradial Nassellaria, where for the most part three interradial or six adradial (sometimes more) apophyses are intercalated between the three primary perradial ones; sometimes here also the ground-form is a quite regular hexagonal or nonagonal pyramid, but usually it is more or less amphithect or amphipleural. Among the eradial Nassellaria, which have no radial apophyses, the ground-form is sometimes allopolar monaxon (conical, ovoid, hemispherical, &c.), sometimes amphithect pyramidal (even in the simplest Stephanida, Archicircus, &c.), or sometimes distinctly zygopleural or bilateral (many Plectellaria).

50. The Ground-Forms of the PhÆodaria.—The PhÆodaria agree with the Nassellaria in the possession of a primitively centraxon ground-form, and like them are monostatic, since a vertical main axis whose basal pole passes through the astropyle is present, owing to the characteristic structure of their cannopylean central capsule. In the great majority of PhÆodaria the spheroidal central capsule also possesses a pair of parapylÆ near the opposite apical pole of the main axis (Tripylea), and these determine (as the right and left secondary openings) an isopolar frontal axis. Hence, strictly speaking, in most PhÆodaria the central capsule has the geometrical ground-form of the amphithect pyramid (as in the Ctenophora), with an allopolar vertical main axis, and two unequal, but isopolar, horizontal transverse axes. In many PhÆodaria the skeleton also has this amphithect pyramidal ground-form, e.g., the bivalved PhÆoconchia and part of the PhÆogromia. On the contrary, in the rest of the PhÆodaria the skeleton exhibits very various geometrical ground-forms, independent of that of the central capsule. In the PhÆosphÆria it forms preferably spheres or endospherical polyhedra, as also in the Castanellida and Circoporida among the PhÆogromia; among the Circoporida there are also seen with remarkable distinctness the regular polyhedra (especially the dodecahedron and icosahedron). Isopolar monaxonia are found among the AulosphÆrida (Aulatractus) and OrosphÆrida; allopolar monaxonia among the Challengerida (Lithogromia). The Medusettida and Tuscarorida show various forms of regular pyramids (allopolar Stauraxonia); and finally, the Challengerida are for the most part centroplanar or bilateral. Thus the PhÆodaria present a great wealth of different geometrical ground-forms in the development of their skeleton, not in that of their central capsule.

Chapter II.—THE CENTRAL CAPSULE.

51. Components of the Central Capsule.—In all Radiolaria without exception, at some period of life or other, the central portion of the soft body is separated from the peripheral portion by an independent, anatomically recognisable membrane; this membrane with all its contents is designated the central capsule, and is the peculiar central organ of the unicellular body, which distinguishes the Radiolaria most clearly from the other Rhizopoda. In the great majority of the Radiolaria the volume of the central capsule is less than that of the surrounding peripheral soft body which we place in opposition to it as "extracapsulum." The "capsule-membrane," which separates these two constituents, arises very early in most Radiolaria, and persists throughout their whole life. In some species, however, the membrane only appears later, immediately before the formation of the spores, and hence is absent for a considerable period. Regarded as a whole, then, the capsule consists of the following parts:—(1) the capsule-membrane; (2) the enclosed endoplasm, or intracapsular protoplasm; (3) the nucleus. But in addition, many other non-essential structures may be enclosed in the central capsule, especially hyaline spheres (vacuoles), fatty spheres, pigment granules, crystals, &c.

The central capsule was first described in my Monograph in 1862 (pp. 69-82) as the most characteristic component of the Radiolarian organism, and distinguished from the whole extracapsular soft body. The fact that it has recently been reported as absent by various authors is due to their having observed young or unripe specimens, before the formation of the spores. In some species of Polycyttaria and Acantharia the membrane persists only a very short time.

53. The Secondary Forms of the Central Capsule.—The original purely spherical form of the central capsule persists only in the minority of the Radiolaria, namely, the greater part of the Spumellaria and Acantharia; it passes over into various other secondary forms in the majority of the class, in the whole of the Nassellaria and PhÆodaria, and in a considerable portion of the Spumellaria and Acantharia. These secondary or derived forms may be divided into two quite distinct groups, which may be designated endometamorphic and exometamorphic; in the former the cause of the divergence of the secondary form from the sphere lies in the internal structure of the central capsule; in the latter it lies in the external influence exerted by the growth of the skeleton. Obviously the former series of modifications is more significant than the latter.

54. The Endometamorphic Forms of the Central Capsule.—The secondary forms of the central capsule, which are due to internal causes connected with its growth, are as follows:—

A. The Ellipsoidal Central Capsule, with one axis elongated, so that it becomes the vertical main axis of the body.

B. The Cylindrical Central Capsule, with considerable elongation of the vertical main axis, which is several times as long as the horizontal transverse axis.

b. Among the Acantharia, some Amphilonchida.

C. The Discoidal, Spheroidal, or Lenticular Central Capsule, with one axis shorter than the others, which becomes the vertical main axis.

a. Among the Spumellaria, Actidiscus (p. 15), Collodiscus (p. 27), and the large group Discoidea (p. 408).

c. Among the Nassellaria, certain Stephoidea and Cyrtoidea.

D. The Lentelliptical Central Capsule (or triaxial ellipsoid), with three unequal but isopolar axes at right angles to each other, the sections in all three dimensions of space being ellipses.

a. Among the Spumellaria, Actilarcus and the large group Larcoidea (p. 604).

b. Among the Acantharia, certain Amphilonchida and Belonaspida.

E. The Polymorphic, Amoeboid or Irregular Central Capsule.

55. The Exometamorphic Forms of the Central Capsule.—The secondary forms of the central capsule, which are brought about by external causes, chiefly dependent on the formation of the skeleton, are very various and in many cases devoid of special interest; in other instances, on the contrary, they are of great importance, because of the clear relation of cause and effect which can be traced between the development of the skeleton and of the capsule. The most important phenomena to be recorded in this connection are as follows:—

The capsule-membrane was first indicated as the most important and absolutely constant component of all Radiolaria, and as the differential character of the class, in my Monograph (1862, pp. 69-71). The careful investigations of R. Hertwig have confirmed this view and at the same time have yielded the most important conclusions regarding the nature and systematic significance of the openings in the capsule (op. cit., 1879, pp. 105-107). On the contrary, Karl Brandt has recently propounded the theory that the capsule-membrane is by no means a constant part of the Radiolarian organism, but is lacking in certain species of Collozoum and SphÆrozoum (1881, p. 392). This contradiction is explained by the fact that in some Collodaria and Acanthometra the formation of the central capsule takes place much later than in the other Radiolaria, in some species indeed only just prior to the development of the swarm spores. I have recognised the presence of it in all species which I have investigated (more than a thousand), and even in those in which Brandt denies its existence. It is often very delicate and may easily be overlooked, especially when the contents of the capsule are colourless, but in all cases by the prudent application of staining fluids and other reagents its presence may be demonstrated. Even in those cases in which the contour of the capsule was not visible, and its contents appeared to pass without definite boundary into the matrix of the extracapsulum, it was possible by the use of appropriate stains or reagents, which would not penetrate the capsule, or of those solvents which were capable of dissolving its contents and of causing it to swell up like a distended bladder, to recognise the existence of the membrane. Those Radiolaria in which it is truly absent are young animals of species in which the membrane is only formed immediately before sporification, and persists but for a short time (e.g., species of Collozoum, SphÆrozoum, Acanthometra, Acanthochiasma, &c.).

57. The Capsule-Openings of the Peripylea (or Spumellaria).—The capsule-membrane of the Peripylea is generally perforated by extremely fine and numerous pores, which are distributed at equal distances over the whole surface, and are precisely alike in all parts of the capsule. Hence the Spumellaria may be called "Holotrypasta" or "Porulosa"; they agree with the Actipylea in being devoid of an osculum or operculum; they are distinguished from the latter group mainly in that their pores are equally distributed over the whole surface of the capsule, whilst in the Actipylea the pores are disposed in definite groups or lines, separated by large imporous areas.

The central capsule of the Spumellaria, with its innumerable fine and evenly distributed pores, must be regarded as the primitive arrangement, from which the different central capsules of the three other legions have been developed. The central capsule of the Actipylea has been derived from that of the Peripylea by reduction in the number of the pores and their distribution in definite, regularly disposed areas in the membrane. The central capsule of the Osculosa is characterised by the formation of a special main-aperture (osculum) at the basal pole, which is closed in the Monopylea by the porochora, and in the Cannopylea by the astropyle; the remaining pores, with the exception of the accessory openings of many Cannopylea, remain undeveloped in both these legions. In the same way Hertwig regards the central capsule of the Peripylea as the primitive form (1879, L. N. 33, p. 107).

58. The Capsule-Openings of the Actipylea (or Acantharia).—The capsule-membrane of the Actipylea is perforated by very numerous fine pores, which are regularly distributed over the surface of the central capsule, and separated by imporous intervals. Hence the Acantharia belong to the "Holotrypasta" or "Porulosa"; they have neither osculum nor operculum, and agree in this particular with the Peripylea; but they are separated from these latter chiefly by the fact that their pores are much less numerous, and marked off into regularly arranged groups or lines by imporous intervals. In the Peripylea, on the contrary, the pores are much more numerous and are evenly distributed over the whole surface of the capsule.

The central capsule of the Acantharia has hitherto been for the most part confounded with that of the Spumellaria, and no clear distinction has been drawn in this respect between the two legions of the Porulosa. Hertwig, who in 1879 first discovered the remarkably different structure of the Osculosa (Nassellaria and PhÆodaria), recognised no distinction between the structure of the capsules in the Peripylea and Actipylea (his Acanthometrea), and supposed that in both these legions "very fine pores were evenly distributed in large numbers over the capsule-membrane" (loc. cit., p. 106). I have, however, during the last few years convinced myself, by the careful comparative investigation of numerous Acantharia, that in this respect they are quite distinct from the Spumellaria (with perhaps the exception of the Astrolophida, which are nearly related to the primitive Actissa). The number of pores in the Actipylea is usually very much smaller than in the Peripylea, and they are regularly arranged in groups.

The porous area of the Monopylea was first described by Hertwig in 1879, and shown to be the characteristic main-opening of the central capsule in various families belonging to this legion (L. N. 33, pp. 71, 73, 83, 106, Taf. vii., viii.). According to his view "the capsule-membrane in the porous area becomes thickened around each pore into a rod, perforated by a canal," and the intracapsular protoplasm passes outwards through these fine canals (loc. cit., p. 106). I am not able to share this interpretation, but think rather that I have convinced myself by the examination of some living Nassellaria, and of many well-stained and preserved preparations in the Challenger collection, that the rods are solid, specially modified portions of the capsular wall, and that the protoplasm does not pass through them but through pores which lie between them.

The peculiar capsule-openings of the PhÆodaria were first discovered and carefully described by Hertwig in 1879 (L. N. 33, pp. 95, 107). He found in all the six genera which he examined three openings, a main-opening at the basal pole of the main axis and two accessory openings, one on either side of the apical pole; hence he named the whole group "Tripylea." This name, however, is not applicable to the numerous PhÆodaria mentioned above, which have only a main opening without any accessory openings, nor to those genera in which the number of the latter is variable. I have, therefore, replaced Hertwig's designation by the term "Cannopylea," which has reference to the peculiar tubular form of the opening. This I find much more developed in many PhÆodaria than Hertwig has represented, and I must also, in certain particulars, dissent from his delineation of the minute structure, although this is in the main remarkably accurate.

61. The Nucleus.—The nucleus, enclosed in the central capsule of all Radiolaria, behaves in every respect like a true cell-nucleus, and thus lies at the base of the now universal opinion, that the whole Radiolarian organism, in spite of its varied development and remarkable variations, is unicellular and remains throughout life a true individual cell. This important theory is not invalidated by the fact that the nucleus undergoes peculiar modifications in many groups, and in certain groups presents appearances seldom or never seen elsewhere.

62. Uninuclear and Multinuclear Radiolaria (Monocaryotic and Polycaryotic).—All Radiolaria present two different conditions in respect of the behaviour of the nucleus, since in their young stages they are uninuclear (monocaryotic), and in later stages multinuclear (polycaryotic). This is readily explained by the fact that each individual Radiolarian is developed from a simple unicellular swarm-spore, and that afterwards, before the formation of swarm-spores, the single nucleus divides into many small nuclei. Thus in the Radiolaria the nucleus is pre-eminently the organ of reproduction and inheritance. The division of the originally single nucleus into many small nuclei may take place, however, at very different periods, so that the Radiolaria may be divided in this respect into precocious and serotinous.

64. Central and Excentric Nuclei.—The position of the nucleus in the interior of the central capsule was no doubt primitively central, and this situation in the geometrical centre of the original spherical central capsule has been accurately retained in all monozootic Spumellaria; in the polyzootic families of this legion (Polycyttaria), on the contrary, it is obscured by the precocious division of the nucleus. In the other three legions, which may be phylogenetically derived from the Spumellaria, the position of the nucleus is rarely central, but usually excentric, or at most subcentral. In the Acantharia (both Acanthometra and Acanthophracta) the central position of the nucleus is at once excluded by the constantly centrogenous development of the skeleton; the nucleus is therefore always excentric, and may lie at either side; it usually divides very early into numerous separate nuclei, which are usually distributed in the peripheral portions of the central capsule. In the Nassellaria the development of the porochora, and of the podoconus which stands upon it, brings about the formation of a vertical axis, and in consequence the central capsule assumes a monaxon form (usually ovoid or conical); the nucleus then lies in the main axis, but excentrically between the apex of the podoconus and the aboral pole. In many Nassellaria, however, especially when the podoconus is so large that its apex approaches the aboral pole of the central capsule, the nucleus is pressed to one side and lies quite excentrically. The PhÆodaria exhibit a different arrangement; the large spheroidal nucleus is always subcentral, so that its main axis corresponds with that of the concentric spheroidal central capsule; but since the astropyle always occupies the oral pole of the latter, and since the distance of the nucleus from this pole is always somewhat different from its distance from the other, it follows that, strictly speaking, the nucleus never lies accurately in the geometrical centre.

65. Homogeneous and Allogeneous Nuclei.—The nucleus of the Radiolaria not only exhibits a similar structure and composition, and suffers similar modifications to those which are found to occur in the case of other cell-nuclei, but also to some extent shows very peculiar developmental forms, which are seldom or never found in other cells. In the first place the nuclei may be divided into homogeneous and allogeneous, the former are structureless and consist of a uniform mass of nuclein, whilst the latter are composed of different substances and show various structural relations. Homogeneous nuclei, whose whole mass is uniform and exhibits no structural differentiation, are probably always to be found in the swarm-spores; in the fully developed Radiolarian body they are found only in the first legion, Spumellaria, and that both in many Monozoa (especially small SphÆroidea and Prunoidea) and in the Polyzoa (or Polycyttaria). The whole mass of these homogeneous nuclei, which are usually spherical or ellipsoidal, consists of uniform, perfectly clear and transparent nuclein, and becomes evenly stained by carmine, hÆmatoxyline, &c. They may be readily distinguished by these means from the clear vacuoles or "hyaline vesicles," which are evenly distributed in the endoplasm of many Radiolaria, and may be confused with the former. Allogeneous nuclei, which are always composed of different parts and often show complicated structural relations, are found developed in the great majority of Radiolaria. The most important differentiation exhibited by these secondary forms is the separation of the nuclear mass into a firm nuclear substance (caryoplasm) and a fluid nuclear juice (caryolymph). In addition in each nucleus a nucleolus is visible, and often several or many may be seen (see §§ 67 to 70).

66. The Form of the Nucleus.—The nucleus of the Radiolaria shows greater variations in form and structure than are to be found in the majority of cell-nuclei; exception must, however, be made in the case of many animal ovicells, which, in their peculiar form and composition, often recall large Radiolarian nuclei. With respect to the external shape two main forms may be distinguished, as primary and secondary. The primary form of the Radiolarian nucleus is the sphere; it occurs not only in most swarm-spores, but also in most adult forms belonging to the legion Spumellaria, and in individual instances in other groups; indeed the nuclei of most Spumellaria, as also the concentric central capsules in which they lie, are true geometrical spheres. The secondary forms of the nucleus are found in the majority of adult Radiolaria, and arise from the primary spherical forms in various ways, either by the elongation or contraction of one axis, or by the formation of apophyses or processes. The most important of these secondary forms are as follows:—

1. Ellipsoidal nuclei, arising by elongation of one principal axis; very common among the Nassellaria, as well as in many Prunoidea and Larcoidea among the Spumellaria; also in several Acantharia.

2. Discoidal nuclei, arising by contraction of one principal axis, sometimes lenticular or spheroidal, biconvex, sometimes shaped like a disc or coin; especially common in the Discoidea among the Spumellaria, also in some Acantharia; the large nucleus of the PhÆodaria is always spheroidal or almost spherical, with a slightly shortened main axis.

4. Amoeboid nuclei, with unequal processes irregularly arranged, in certain irregular forms of Spumellaria and Acantharia.

Both the simple serotinous nucleus of the monozootic Spumellaria, and the numerous precocious nuclei of the Polycyttaria, were first described in my Monograph in 1862, the former as the "endocyst" ("Binnen-BlÄschen"), the latter as "spherical transparent vesicles" ("Kugelige wasserhelle BlÄschen"). I was in error, however, in regarding the latter as identical with the so-called "hyaline spherules" in the central capsule of many Monozoa, which rather belong to the category of intracapsular vacuoles (see § 72). The credit of recognising, by the aid of the modern methods of staining, the distinctness of these two structures, which may readily be mistaken for each other, and of demonstrating the true nature both of the serotinous and precocious nuclei, belongs to Richard Hertwig (1879, L. N. 33).

A. The numerous nuclei, which are to be found in the central capsule of most mature Acantharia, were first described in my Monograph (1862) as "spherical, transparent vesicles, provided with a small dark granule" (p. 374, Taf. xv. figs. 2, 5; Taf. xvi. figs. 2, 4; Taf. xxi. fig. 7, &c.). Their more minute constitution and peculiar origin were first accurately delineated by R. Hertwig (1879, loc. cit., pp. 11-24, Taf. i-iii.).

B. The fact that in a number of Acantharia the nucleus does not divide early as in the majority of the legion, but only at a later period, was first observed by R. Hertwig in a species of Acanthometra (Xiphacantha serrata), and a species of Acanthophracta (Phatnaspis mÜlleri = Haliommatidium mÜlleri) (loc. cit., pp. 11 and 27). This serotinous division of the nucleus seems, however, to be rather widely spread in both sublegions of the Acantharia; I have found, not only in the forms above mentioned, but also in several others belonging to different genera, a single large excentric nucleus, even in those individuals in which the skeleton was fully developed.

The numerous small, spherical, homogeneous nuclei which are to be found in the central capsules of those Nassellaria, which are ripe and about to develop spores, were described in 1862 in my Monograph, as "numerous, small, transparent, spherical cells" in the case of various Cyrtoidea (Arachnocorys, Lithomelissa, Eucecryphalus, Eucyrtidium, &c.) (loc. cit., pp. 302, 305, 309, 321, &c.), and I find them of the same form and dimensions, but deeply stained with carmine in many preparations in the Challenger collection. R. Hertwig has delineated them very accurately in the case of Tridictyopus (1879, loc. cit., p. 84, Taf. vii. fig. 3). He was also the first to recognise the uninucleate condition of the Nassellaria, which is much more frequently observed than the serotinous multinucleate condition, and he described very clearly the peculiar lobed nuclei which arise in Cyrtoidea, owing to the protrusion of the nucleus through the cortinar septum (loc. cit., p. 85, Taf. viii. figs. 3-8).

The large nucleus of the PhÆodaria was first described in my Monograph in 1862, in the case of Aulacantha (p. 263), AulosphÆra (p. 359), and Coelodendrum (p. 361), as a "large, spherical, thin-walled endocyst," from 0.1 to 0.2 mm. in diameter. More detailed descriptions, especially with respect to the behaviour of the nucleoli were given by R. Hertwig in 1879 (L. N. 33, p. 97).

71. The Endoplasm or Intracapsular Protoplasm.—In all Radiolaria the intracapsular protoplasm, which, for the sake of brevity, may be termed "endoplasm," constitutes originally, and especially in the earliest stages, the only important content of the central capsule, except the nucleus. In certain Spumellaria and Nassellaria, of simple structure and of small dimensions, this condition persists for a long period, and the endoplasm then appears as a homogeneous, colourless, turbid or finely granular, mucous, semi-solid mass, which cannot be distinguished from the ordinary undifferentiated protoplasm of young cells; no definite structure, and in particular, no fibrillar network, can be discovered in it even by the use of the customary reagents. In the great majority of the Radiolaria, however, this primitive homogeneous condition of the endoplasm is very transient, and it soon undergoes definite modifications, becoming differentiated into separate parts or producing new constituent contents. Such products of the internal protoplasm are in particular hyaline spheres (vacuoles and alveoles), oil-globules, pigment-bodies, crystals, &c. The most important of the differentiations which take place in the endoplasm is that into an internal, granular, medullary substance and an external, fibrillar, cortical substance; although the various legions behave somewhat differently in this respect (§§ 77-80).

B. The "albumen spheres," which were first observed by A. Schneider in 1858 in the common cosmopolitan Thalassicolla nucleata (L. N. 13, p. 40), and which appear to occur in only a few other Thalassicollida, are distinguished from the ordinary hyaline spheres of about the same size by their higher refractive power and by certain albuminoid reactions, especially the coagulation of a membranous envelope under the influence of certain reagents (see my Monograph, p. 250, and Hertwig, L. N. 26, 1876, p. 46). They often enclose various formed contents, and require further investigation.

C. The gelatinous spheres of various sizes, found in the endoplasm of the Radiolaria, agree in their reactions (especially in staining by certain reagents) with the common extracapsular jelly of the calymma, and are hence distinguishable both from the true (coagulable) "albumen sphere," and from the ordinary watery vacuoles.

74. The Intracapsular Pigment-Bodies.—In the majority of Radiolaria when observed alive, the central capsule is coloured, only in the minority is it colourless. The colour is never diffuse, but always due to the formation of definite pigment granules or vesicles, which are sometimes distributed evenly throughout the endoplasm, sometimes aggregated in the central or peripheral regions. Their form may be either spherical, irregularly rounded, or polyhedral. They vary much in dimensions, but in most cases are immeasurably small, and appear under a high magnifying power as fine dust; occasionally, however, their diameter may amount to from 0.001 to 0.005 or more. The chemical constitution of the intracapsular pigment is unknown in most Radiolaria, and is probably very various. In many instances the pigment-granules consist of fat, in others not. The commonest colours are yellow, red, and brown; violet and blue are rare, and green still rarer. Sometimes a definite tone of colour prevails throughout a whole group, and may then be attributed to inheritance, e.g., red is found in most SphÆroidea, and blue in the Polycyttaria (see note A). One colour is almost always constant in the members of the same species. True pigment-cells, belonging to the Radiolarian organism, do not occur within the central capsule. The peculiar yellow cells which are found in the central capsule of many Acantharia are symbiotic xanthellÆ (see § 76).

A. The number of Radiolaria whose pigment has been examined in the living state, is too small to allow of any general conclusions being drawn. Regarding the different colours known, see my Monograph, L. N. 16, p. 76.

A. The amyloid concretions of Thalassicolla nucleata have been described in detail in my Monograph (pp. 80, 250, Taf. iii. figs. 2, 3), and by R. Hertwig in the Histologie der Radiolarien (1876, p. 47, Taf. iii. figs. 9-13).

B. The violin-shaped concretions of ThalassosphÆra bifurca have been figured in my Monograph (pp. 80, 261, Taf. xii. fig. 1).

76. The Intracapsular XanthellÆ.—The xanthellÆ, zooxanthellÆ, or symbiotic "yellow cells" are found within the central capsule only in the Acantharia, whilst in other Radiolaria they only occur in the extracapsulum. They are most frequent in the Acanthometra, rarer in the Acanthophracta, but even in the former they are often wanting. Their number is very variable, but usually small, from ten to thirty in one capsule. They lie for the most part immediately below the capsule membrane, in the cortical layer of the endoplasm. The form of the yellow cells is either spherical or ellipsoidal, often also spheroidal or even lentiform. The diameter varies from 0.01 to 0.03 mm. They possess a distinct membrane and an excentric nucleus, and contain numerous yellow pigment-granules in the endoplasm. This yellow pigment dissolves in mineral acids to form a green fluid, and in other respects also behaves somewhat differently from the yellow pigment in the extracapsular yellow cells of the Spumellaria and Nassellaria. In both cases, however, the xanthellÆ are not integral portions of the organism, but unicellular algae, living as parasites or symbiontes in the body.

A. The yellow cells in the central capsule of the Acantharia were first observed by Joh. MÜller (L. N. 12, pp. 14, 47). In my Monograph I described them at greater length, and indicated their differences from the extracapsular yellow cells of other Radiolaria (L. N. 16, pp. 77, 86). Since then, R. Hertwig has demonstrated their cellular nature (L. N. 33, pp. 12, 113), and still more recently Brandt has given further accurate information regarding their occurrence, constitution, and physiological significance (L. N. 39, ii. Art., p. 235, figs. 62-73).

A. The radial structure of the endoplasm was first described in my Monograph (1862, p. 74), though R. Hertwig (1879, p. 112) was the first to indicate its typical significance in the case of the Peripylea, and to demonstrate its causal relation with the radial currents in the central capsule of this legion. More recent investigations have led me to the conviction that this phenomenon is more widespread, and often more strongly developed, than was formerly imagined, and that it is probably one of the typical characters of all Spumellaria (at least of the Monozoa).

B. The centripetal cones of Physematium, which have hitherto been known only in these colossal ThalassosphÆrida, were fully described in my Monograph under the name "conical centripetal cell-groups"; by their first discoverer, A. Schneider (L. N. 13), they were termed "nests," and compared with the "nests" (central capsules) of the Polycyttaria. In the Physematium mÜlleri of the Mediterranean (hitherto only observed by Schneider and myself at Messina) it appeared as though each centripetal cone were composed of a group of from three to nine (usually four or five) slender wedge-shaped cells, whose common centripetal apex was produced into a radial thread of sarcode (L. N. 16, p. 258, Taf. iii. fig. 7). Since then (1866) I have observed at Lanzerote, in the Canary Islands, a nearly related form, which I take to be Physematium atlanticum, Meyen. In this, however, the "centripetal cell-groups" were wanting, and the whole cortical layer of the endoplasm was cleft into numerous radial portions, each enclosing a nucleus (probably the mother-cells of flagellate spores, see p. 35).

C. The radial fibres of the medullary endoplasm which cling to an extracted nucleus have been observed by Hertwig in certain SphÆroidea (DiplosphÆra, ArachnosphÆra) (L. N. 33, p. 40).

78. The Endoplasm of the Actipylea.—The intracapsular protoplasm of the Acantharia or Actipylea is often distinguished by a partial or complete radial arrangement like that of the Peripylea, but differing in the number, size, form, and distribution of the radial portions into which the endoplasm is differentiated. For since the pores of the capsule membrane are distributed at equal distances all over the surface in the Spumellaria, whilst in the Acantharia they are arranged in definite groups, and since the number and arrangement of the pores has a direct influence upon the internal currents of the endoplasm, it follows that the radial structure in the latter legion must be very different from that in the former. In addition to this there must not be forgotten the important influence which the early centrogenous formation of the skeletal rods exercises upon the disposition and growth of the intracapsular structures. Hence the endoplasm of the Acantharia does not separate into innumerable thin, closely packed radial wedges or cortical radial rods, but into a small number of large pyramidal portions between which run the radially disposed heterogeneous portions of the contents of the capsule, viz., the radial bars of acanthin and the peculiar intracapsular "axial threads." As a direct consequence of the regular disposition of these heterogeneous radial portions, which is often characteristic of the various families of the Acantharia, a corresponding differentiation of the endoplasm is brought about; it divides into a number of conical or pyramidal portions (radial pyramids), whose bases rest upon the capsule-membrane and whose apices are directed towards the centre of the capsule (the central star of the skeleton). These radial pyramids are, however, but rarely visible, being usually more or less concealed by a dark pigment.

The differentiations of the endoplasm in the central capsule of the Actipylea have been but little investigated, but they appear to vary somewhat in the different groups of this legion. In all Acantharia in which the twenty radial bars are regularly arranged according to the MÜllerian law (see p. 717) and in which axial threads constant in number and disposition run between them from the central star to the capsule-membrane, it obviously follows that the endoplasm must be divided into more or less distinct radial pyramids, and this must the case whether these take the form of continuous tracts or of actually separable portions. The regular polygonal figures, often seen on the surface of the central capsule (with special distinctness in Acanthometron elasticum and Acanthometron pellucidum) separated by a network of granular threads, are the bases of such radial pyramids (see Hertwig, L. N. 43, p. 12, Taf. i. figs. 1-7).

A. The podoconus of the Monopylea was first described by R. Hertwig in 1879, and recognised as a characteristic component of the central capsule in the most various groups of this legion (in Plectoidea, Stephoidea, Spyroidea, and Cyrtoidea; see his figures, loc. cit., Taf. vii., viii., and the description, pp. 71, 73, 83, 106). Hertwig called it the "pseudopodial cone," and regarded it as a conical process of the capsule-membrane, which is developed from this latter and projects from the porous area into the interior of the central capsule; "it is penetrated by fine canals which arise at the apex of the cone, diverge towards the base, and terminate there in the rods of the pseudopodial area. The intracapsular protoplasm penetrates at the apex of the pseudopodial cone into its fine canals, runs along them and emerges from the rods of the porous area in the form of slender threads" (loc. cit., p. 19). I cannot agree with this view of Hertwig, although I have been able to confirm the accuracy of his description by my own observations upon numerous excellently stained and preserved preparations in the Challenger collection. As I have proved by numerous teased out preparations, and as Hertwig himself correctly states, "the cone is more readily detached from the membrane than from the protoplasm, when the capsule is teased" (loc. cit., p. 73). Hence I regard the podoconus not as a differentiated portion of the capsule-membrane but as endoplasm, and believe that it is composed of myophanes or "contractile muscular fibrils" in the same manner as the cortical layer of the Cannopylea. Probably the contraction of these fibrils serves to raise the opercular rods and hence to allow the exit of the endoplasm through the pores which lie between these opercular rhabdillae (compare § 59).

A. The fine fibrillÆ in the cortical layer of the endoplasm were first described by Hertwig in 1879 (L. N. 33, p. 98, Taf x. figs. 6-10). He found them, however, only below the three openings in the capsule of the Tripylea, where they form three stellate groups of fibrils. I find them very clearly shown, and with especial distinctness, under the astropyle in most PhÆodaria of which I have had the opportunity of examining well-stained and preserved central capsules. In many cases, also, the striation is not confined to the apertures, but spreads over the whole cortical layer. Perhaps this constitutes in all PhÆodaria a thin myophane-sheet, whose contractile fibrils run from one pole of the main axis to the other and cause by their contraction changes in the form of the spheroidal central capsule.

B. The granular medullary portion of the endoplasm of the PhÆodaria, with its numerous clear spherical vacuoles, was first described in my Monograph (1862), in the case of Aulacantha (p. 263), AulosphÆra (p. 359), and Coelodendrum (p. 361) as a "finely granular, mucous substance (intracapsular sarcode), packed more or less closely with clear spherical vesicles from 0.005 to 0.015 mm. in diameter, each of which contains one or two, rarely three, dark shining granules." That these clear spheres are true vacuoles was first clearly proved by Hertwig (L. N. 33, p. 98). As a rule all the vacuoles of the same central capsule are of equal size (generally from 0.008 to 0.012 mm. in diameter), and are distributed at equal intervals throughout the finely granular endoplasm.

Chapter III.—THE EXTRACAPSULUM.

(§§ 81-100).

81. The Components of the Extracapsulum.—The extracapsulum or extracapsular malacoma, under which name are included all those parts of the soft body which lie outside the central capsule, consists of the following constant, and important constituents:—(1) The calymma or extracapsular jelly-veil; (2) the sarcomatrix or layer of exoplasm immediately surrounding the membrane of the central capsule; (3) the sarcodictyum or network of exoplasm, covering the surface of the calymma; (4) the pseudopodia or radial fibres of exoplasm, which may again be subdivided into intracalymmar pseudopodia, uniting the sarcomatrix and sarcodictyum, and extracalymmar pseudopodia, radiating freely into the water outside the calymma.

82. The Calymma.—The calymma or extracapsular jelly-veil of the Radiolaria is always the most voluminous portion of the extracapsulum, and in spite of its simple structureless constitution is of great morphological and physiological importance. In all Radiolaria this gelatinous mantle completely surrounds the central capsule, but is separated from its outer surface by a continuous, though thin, layer of exoplasm, the sarcomatrix. The pseudopodia radiating from the latter pierce the calymma, form the sarcodictyum at its surface, and radiate from its nodal points freely into the surrounding water. The calymma is rarely visible in living freshly captured Radiolaria, examined in sea-water, for its gelatinous substance is perfectly hyaline, colourless and pellucid, and possesses the same refractive index as sea-water; but when the object is removed from this fluid and transferred to carmine solution or some other colouring matter, the extent and figure of the calymma become apparent, for the staining fluid does not at first penetrate into the gelatinous material. When this has taken place, however (after a longer or shorter time), and the gelatinous material has become coloured, its form and size may be observed by the converse experiment; the object is transferred once more to water and the outlines of the calymma become as clear as those of the central capsule. The same is the case with dead specimens in which the sticky surface of the calymma has become covered with dust.

The jelly-veil of the Radiolaria was recognised even by the earliest observers of the group, Meyen (1834), and Huxley (1851), and compared with that of the Palmellaria; the former noticed it in Physematium and SphÆrozoum (L. N. 1, p. 283), and the latter in Thalassicolla and CollosphÆra (L. N. 5, p. 433). In all these Spumellaria, both in the monozootic Thalassicolla and in the polyzootic SphÆrozoum and CollosphÆra, the calymma is very voluminous and filled with large alveoli. Meyen called them "muco-gelatinous masses, in the interior of which are contained small equal-sized vesicles"; Huxley likewise found clear vesicles in the jelly and compared them with Dujardin's vacuoles. Johannes MÜller observed the jelly-veil in many different Radiolaria, in particular in the Acanthometra, first discovered by him, but erroneously believed that it only originated after death by liquefaction of the sarcode (L. N. 12, p. 6). This mistake is, however, easy to understand, since in living Radiolaria the calymma is usually invisible on account of its perfect transparency, whilst in dead specimens it is usually quite distinct on account of the dust clinging to its adhesive surface. I myself believed that the formation of the voluminous hyaline jelly-veil was only partially due to liquefaction after death, but that it was to some extent present in the living organism and that it might vanish and subsequently reappear by means of imbibition (L. N. 16, pp. 109, 110). R. Hertwig was the first to demonstrate, in 1879, that the jelly-veil is constantly present in living Radiolaria, that it forms the basis of the extracapsular malacoma and surrounds the central capsule as a second protective sheath (L. N. 33, p. 114).

84. The Consistency of the Calymma.—The gelatinous material of which the calymma of the Radiolaria consists is a pellucid mass, rich in water and usually quite hyaline and structureless; its consistency is very variable. In the majority of the Radiolaria it may perhaps be about equal to that of the jelly which composes the umbrella of most MedusÆ; but as in these latter it may vary between very wide extremes, constituting on the one hand a very soft jelly-mantle, offering but little resistance to mechanical influences and almost disintegrating under the eyes of the observer, and on the other hand forming a firm gelatinous shell, comparable to cartilage in hardness, elasticity, and power of mechanical resistance. In many Radiolaria of large dimensions with an alveolar calymma (especially in numerous Collodaria and PhÆodaria) this may be split by means of dissecting needles and the central capsule extracted like the stone from a cherry, and then it is easy to ascertain that the firmness and elasticity of this jelly-veil are not less than those of a cherry. The different degrees of consistency in the various Radiolaria may be dependent either upon the relative amount of water which they contain, or upon qualitative or quantitative variations in the organic substance of which the jelly consists. Great importance is to be attached to the considerable consistency of the calymma, because it furnishes the indispensable groundwork for the deposition of many parts of the skeleton and particularly of the lattice-shells.

85. The Primary and Secondary Calymma.—In most Radiolaria the external form and volume of the calymma are different at different stages of growth, and this difference is mainly dependent upon the development of the skeleton. Hence it is advisable to distinguish in general the primary from the secondary calymma. The primary calymma is in the great majority of Radiolaria a perfect sphere, in the middle of which lies the concentric central capsule; on the surface of this gelatinous plate the primary spherical lattice-shell is secreted in most Spumellaria and Acanthophracta, as well as in those PhÆodaria which possess a spherical shell; in the remaining PhÆodaria also and in the Nassellaria, where the lattice-shell is not spherical but monaxon, it is secreted on the surface of the primary calymma. This takes place at a definite time, very important in the development of the Radiolarian, which for the sake of brevity we shall term the "lorication-period." Since the firm surface of the primary calymma furnishes the necessary foundation for the deposition of the primary lattice-shell, it is of the greatest mechanical significance in all shell-bearing Radiolaria. The secondary calymma arises only after the lorication-period by further growth of the primitive jelly-mantle and in the fully developed Radiolarian usually encloses wholly or partially the external parts of the skeleton, in consequence of which it assumes the most various forms. Very often the secondary calymma is polyhedral, being stretched between the radial spines of the skeleton, the distal ends of the latter then forming the fixed points of the gelatinous polyhedron.

A. The extracapsular vacuoles in the calymma were first observed in 1851 by Huxley, in Thalassicolla and SphÆrozoum, and compared with Dujardin's sarcode vacuoles (L. N. 5). Afterwards J. MÜller noticed that generally these "large clear vesicles are covered by a fine membrane," and hence he called them "alveoles" (L. N. 12, pp. 3, 7, &c.). In my Monograph I have described them more in detail as "extracapsular alveoles" (1862, p. 88, Tafs. i.-iii. xxxii.-xxxv.). Ever since then the point has been debated whether these clear spaces are simple vacuoles in the sense of Huxley or vesicular alveoles as stated by J. MÜller. This contention is unnecessary, for both varieties are present, and often no sharp line can be drawn between them. R. Hertwig has recently come to the conclusion that they are as a rule "membraneless vacuoles," but that they "sometimes become surrounded by a special envelope" (L. N. 33, p. 31). He even succeeded "in extracting from a CollosphÆra the large vesicle which lies in the centre of many colonies and removing its covering of central capsules and jelly."

B. The mechanical importance of the alveolar structure, which certainly increases the elasticity and mechanical resistance of the voluminous calymma, has not yet been sufficiently realised; in the case of those Radiolaria which have no skeleton, or at all events no lattice-shell, it may take the place of this as a protective envelope. Furthermore, by taking in and giving out water it may discharge a hydrostatic function, causing the organism to rise or sink in the water.

On the extracapsular pigment of Thalassicolla nucleata, compare my Monograph, pp. 87, 251. On the red extracapsular pigment-granules of the Acantharia, see L. N. 19, pp. 345, 364, &c.

A. The phÆodium of Aulacantha, Thalassoplancta, and Coelodendrum was first described in 1862, in my Monograph, as an excentric extracapsular mass of pigment of blackish-brown or olive-green colour (pp. 87, 262, 264, 361, Taf. ii. iii. xxxii.). Since then John Murray, who investigated many living PhÆodaria during the Challenger expedition, has shown its general distribution in this legion (Proc. Roy. Soc. Lond., vol. xxiv. p. 536, 1876). From the constancy of its presence I gave the legion the name PhÆodaria in 1879 (L. N. 34).

C. Perhaps the phÆodellÆ are to some extent symbiontes with the PhÆodaria; the xanthellÆ present in most other Radiolaria are absent in this legion.

90. The Extracapsular XanthellÆ.—XanthellÆ or ZooxanthellÆ, symbiotic "yellow cells," are very commonly found in the extracapsulum of the Radiolaria, especially in many Spumellaria and Nassellaria; whilst in the Acantharia similar yellow cells usually only occur within the central capsule, and in the PhÆodaria their presence has not been certainly demonstrated. The extracapsular XanthellÆ are found most abundantly in the Collodaria, both in the monozootic Thalassicollida and in the polyzootic SphÆrozoida. They occur in smaller numbers in the SphÆrellaria, and in many divisions of the latter they seem to be entirely absent. Also it sometimes happens that, though present in large numbers in some Spumellaria, they are entirely absent in others nearly related to them; indeed, this has also been observed in the case of different individuals of the same species. This fact alone is sufficient to show that the XanthellÆ are not an integral part of the Radiolarian organism (as was formerly believed) but parasites or more correctly symbiontes, which live as inhabitants of the calymma. More recent investigations have shown, that besides the yellow pigment-grains they contain starch or an amyloid substance, that is to say, vegetable reserve materials, that their thin envelope contains cellulose, and that their yellow colouring-matter resembles chlorophyll and is related to that of the DiatomaceÆ ("Diatomin"). Hence they are now generally regarded as unicellular AlgÆ, nearly related to those which occur as symbiontes in other marine animals (Exuviella, &c.). The starch, which they develop with the formation of oxygen, may serve as nutriment to the Radiolaria, while the carbonic acid yielded by the latter is also beneficial to the XanthellÆ. The form of the XanthellÆ is usually spherical and elliptical, often also sphÆroidal or discoidal. Their diameter is usually between 0.008 and 0.012 mm., rarely more or less. The differences exhibited by XanthellÆ which live in different groups of Radiolaria demand further investigation, which will perhaps lead to the establishment of several species of the genus Zooxanthella. At present Zooxanthella extracapsularis, in the calymma of Spumellaria and Nassellaria, may be clearly distinguished from Zooxanthella intracapsularis, in the central capsule of the Acantharia.

The "yellow cells" were first described in 1851 by Huxley, in the Collodaria, and afterwards by J. MÜller (1858) in many Spumellaria and Nassellaria. In my Monograph (1862, pp. 84-87) I gave a detailed account of their structure and increase by division, and laid special emphasis on the fact that they are the only elements in the Radiolarian organism which "are undoubtedly cells in the strict histological sense of the word." Afterwards, in my BeitrÄge zur Plastiden-Theorie, I showed the constant presence of "starch in the yellow cells of the Radiolaria" (1870, L. N. 21). Shortly afterwards Cienkowski observed that the yellow cells live independently and reproduce themselves after the death of the Radiolaria, and in consequence first put forth the hypothesis that they do not belong to the Radiolarian organism, but that they are unicellular AlgÆ parasitic upon it (1871, L. N. 22). This view was ten years later more fully established by Karl Brandt, and elucidated by comparison with the symbiosis of the gonidia of AlgÆ, and the hyphÆ of Fungi in the formation of Lichens, which had in the meantime become known (1881, L. N. 38). Brandt gave this unicellular yellow Alga the name Zooxanthella nutricola, and afterwards gave fuller details regarding its remarkable vital relations (L. N. 39). Patrick Geddes, who named it Philozoon, supplemented this account and showed experimentally that it gives off oxygen under the influence of sun-light (1882, L. N. 42, 43). In consequence of this there is no doubt that all XanthellÆ (the Zooxanthella extracapsularis of Spumellaria and Nassellaria, and the Zooxanthella intracapsularis of the Acantharia, and possibly also the Zooxanthella phÆodaris of the PhÆodaria) do not originally belong to the Radiolarian organism, as was believed up to the time of Cienkowski, but penetrate actively into it from without, or are taken in passively by means of the pseudopodia. In any case their symbiosis, when they are associated with the Radiolarian cell in large numbers, may be of great advantage to both parties, since the metastasis of the Xanthella is vegetable, that of the Radiolarian animal in character. In any case their symbiosis is to a large extent accidental, by no means as necessary as in the case of the Lichens. See on these points in addition to Brandt and Geddes (loc. cit.) also Geza Enz, Das Consortial-VerhÄltniss von Algen und Thieren, Biol. Centralbl., Bd. ii. No. 15, 1883, Oskar Hertwig, Die Symbiose oder das Genossenschaftsleben im Thierreich, Jena, 1883, and BÜtschli, Die Radiolarien, in Bronn's Klass. u. Ord. d. Thierreichs, 1882 (L. N. 41, pp. 456-462).

91. The Exoplasm or Extracapsular Protoplasm.—The extracapsular protoplasm, which may be shortly termed the "exoplasm" (or ectosarc), is primitively in all Radiolaria (and especially in their earliest development stages) the only important constituent of the extracapsulum, besides the calymma. Although the extracapsular and intracapsular protoplasm of the Radiolaria are everywhere in direct communication, and although the openings in the membrane of the central capsule bring about an interchange between them, still the two portions of sarcode show certain constant and characteristic differences, which are due to the physiological division of labour between the central and peripheral parts of the body and their corresponding morphological differentiation. The extracapsular, like the intracapsular, protoplasm is originally homogeneous, but may afterwards become differentiated in various ways, producing the special constituents of the extracapsulum. Such "external protoplasmic products" are vacuoles, pigment-bodies, &c. More important, however, are the topographically different sections into which the exoplasm may be divided according to its relations to the central capsule and the calymma. In this respect the following parts may be generally distinguished—(1) the Sarcomatrix, or fundamental layer of the exoplasm, which surrounds the central capsule as a continuous sheath of sarcode and separates it from the calymma; (2) the Sarcoplegma, an irregular network of the exoplasm, which spreads throughout the gelatinous material of the calymma; (3) the Sarcodictyum or network of sarcode on the outer surface of the calymma; and (4) the Pseudopodia, which project outwards from the latter and radiate into the water.

92. The Sarcomatrix.—The sarcomatrix, being "the fundamental layer of the pseudopodia" (or "matrix of the exoplasm"), constitutes the proximal innermost section of the extracapsular sarcode, and in all Radiolaria forms a thin continuous mucous layer, which covers the whole outer surface of the central capsule and separates it from the surrounding calymma (see note A, below). The sarcomatrix communicates internally through the openings of the central capsule with the endoplasm, whilst externally the pseudopodia or mucous threads arise from it, which by their union form the sarcoplegma. The sarcomatrix is only interrupted in the Spumellaria and Acantharia by those parts of the skeleton which perforate the membrane of the central capsule. In all Nassellaria and PhÆodaria, as in the Collodaria, it appears as a perfectly continuous sarcode-envelope of the central capsule. Its thickness is variable; in general it is most strongly developed in the Spumellaria and PhÆodaria, less so in the Nassellaria, and is thinnest in the Acantharia. The thickness seems, however, to vary even in one and the same individual, the difference depending partly upon the different stages of development and partly upon nutritional conditions. After abundant inception of nutriment the thin protoplasmic layer of the matrix is thickened and turbid, rich in granules and irregular masses, which are probably due to enclosed but only half-digested food; xanthellÆ also, as well as foreign bodies taken up with the nutriment, such as frustules of Diatoms and shells of smaller Radiolaria, and of pelagic infusoria, larvÆ, &c., are often, especially in large individuals, aggregated in considerable quantities in the matrix. After long fasting, on the contrary, this is poor in these enclosed bodies and in granules; it then forms a thin colourless more or less hyaline mucous coating to the central capsule. From a physiological standpoint the sarcomatrix is to be regarded as the central organ of the extracapsulum, and as of pre-eminent significance. Probably it is not only the most important organ for the nutrition of the Radiolaria (especially for digestion and assimilation in particular), but perhaps is also the central organ of perception. On the other hand the sarcomatrix belongs to those components of the Radiolarian organism which take no part in the formation of the skeleton.

A. The sarcomatrix was first described in my Monograph in 1862 (p. 110) as the "Mutterboden der Pseudopodien," possessing a pre-eminent physiological importance. Compare also my paper on the sarcode elements of the Rhizopoda (Zeitschr. f. wiss. Zool., Bd. xv. p. 342, 1865).

95. The Pseudopodia.—On the whole the pseudopodia or thread-like processes of the exoplasm exhibit in the Radiolaria the same characteristic peculiarities as in all true Rhizopoda; they are usually very numerous, long and thin, flexible and sensitive filaments of sarcode, which show the peculiar phenomena of granular movement. Their physiological significance is in several respects very great, for they serve as active organs for the inception of nutriment, for locomotion, sensation, and the formation of the skeleton (see note A, below). The presence of a calymma, however, which distinguishes the Radiolaria from the other Rhizopoda, brings about certain modifications in the behaviour of the pseudopodia. If in general all the threads, which arise from the sarcomatrix or fundamental layer and radiate outwards, be called "pseudopodia," then that part of them which is included in the gelatinous substance of the calymma and forms the sarcoplegma may be termed the "collopodia" (or intracalymmar pseudopodia), and the remaining portion, which passes outwards from the sarcodictyum freely into the water, may be described as "astropodia" (or extracalymmar pseudopodia). In many Radiolaria these two portions present some differences in morphological and physiological respects, and certain distinctions are probably generally present (see note B). Apart from this universal differentiation in the different groups of the Radiolaria, specially modified forms of pseudopodia may be recognised as the axopodia and myxopodia of the Acantharia (see § 95, A), and the sarcode-flagellum of certain Spumellaria (see note C).

A. The pseudopodia of the Radiolaria have been so fully described in my Monograph, in 1862, both morphologically and physiologically, that I need only refer to the account there given (pp. 89-127); for supplementary observations see R. Hertwig (1879, L. N. 33, p. 117) and BÜtschli (1882, L. N. 41, pp. 437-445).

B. The Astropodia, or free radiating pseudopodia, are in many Radiolaria more or less clearly distinguishable from the collopodia, which form the sarcoplegma within the calymma; how far these distinctions depend upon a permanent differentiation (especially in the Acantharia and PhÆodaria) needs further investigation.

95A. The Myxopodia and Axopodia.—The two forms of pseudopodia which we distinguish as myxopodia and axopodia differ markedly from each other both morphologically and physiologically. The myxopodia, or ordinary free pseudopodia, which are found in large numbers in all Radiolaria, and constitute their most important peripheral organs, are simple homogeneous exoplasmic threads, which arise from the sarcodictyum or extracalymmar sarcode network, and radiate freely into the water; here they may branch and combine by anastomosis to form a changeable network, but they never contain an axial thread. The axopodia, on the other hand, are differentiated pseudopodia, which consist of a firm radial thread, and a soft covering of exoplasm; they penetrate the whole calymma in a radial direction and project freely from its surface, and generally (if not always) they are produced inwards to the middle of the central capsule, perforating its membrane; their proximal end is lost in a dark central heap of granules. Such axopodia are at present known with certainty only in the Acantharia, where they are widely, and perhaps universally, distributed. Their development in this legion probably stands in direct causal relation to the peculiar structure of the central capsule and the centrogenous formation of the skeleton. Since the radial skeletal rods of the Acanthometra possess originally a thin coating of protoplasm, it may be said that the centrogenous axopodia of this group became differentiated in two ways, the firm axial threads of one section remaining very thin and covered by protoplasm, whilst those of the other section became metamorphosed into radial bars of acanthin. This hypothesis acquires more probability from the regular distribution and arrangement of the axopodia in the Acantharia; they usually stand at fixed intervals between the radial bars, singly or in groups; sometimes their number seems to be not greater than that of the bars, whilst in other cases a circlet or group of axopodia corresponds to each radial bar. Perhaps their fine axial thread consists of acanthin. At all events the axopodia are constant organs (probably sensory, like the "palpocils") and not retractile like the movable myxopodia.

The axial threads in the pseudopodia of the Acanthometra were first discovered by R. Hertwig, who accurately described their peculiar structure and arrangement (L. N. 33, pp. 16, 117).

96. The Myophriscs of the Acanthometra.—The Acanthometra are characterised by a very peculiar differentiation of the exoplasm, namely, by the formation of myophriscs or contractile threads from the sarcodictyum. In most (and perhaps in all) Acantharia of this order each radial bar is surrounded by a circlet of such contractile threads, which was first described as a "ciliary corona" (see note A, below). The number of contractile threads in each circlet usually amounts to from ten to twenty, rarely being more than thirty and less than eight; it often appears to be constant in the individual species (see note B). In the living state the myophriscs are long, thin filaments, the pointed distal end of which is inserted into the radial bar, whilst the thicker proximal end is attached to the surface of the calymma, which is elevated round the base of each rod into the form of a gelatinous cone or skeletal sheath (see note C). Probably the myophriscs lie on the outer surface of the apical portion of this gelatinous cone, and are hence to be regarded as exoplasmic threads differentiated from the sarcodictyum. Sometimes, however (as in Acanthochiasma), they fuse into a contractile membrane and form the envelope of a cone, whose interior is occupied by a gelatinous papilla of the calymma. On mechanical irritation the myophriscs contract rapidly and suddenly, like muscle-fibrillÆ, becoming at the same time thicker, and hence are very different from pseudopodia. Their distal point of insertion being fixed to the firm acanthin rod, they raise by their contraction the skeletal sheath, to which their bases are attached or in the surface of which they lie. The result of their contraction is therefore a distention and increase in volume of the calymma, with which is no doubt connected an inception of water into the gelatinous mass, and hence a diminution in its specific gravity. Probably the Acanthometra contract their myophriscs voluntarily when they wish to rise in the water; when these relax the calymma collapses owing to its elasticity, water is then expelled and the specific gravity increases. From a physiological point of view, then, the myophriscs are to be regarded as a hydrostatic apparatus, morphologically as myophanes or muscular fibrillÆ, such as also occur in the intracapsular protoplasm (see §§ 77-80). On more violent irritation and after the death of the Acanthometra the myophriscs separate from the radial bars and remain attached to the distal ends of the conical gelatinous sheaths as free "ciliary coronas." At the same time, they melt into short, thick, hyaline rods, the so-called "gelatinous cilia." The myophriscs are found only in the order Acanthometra, and are wanting in the Acanthophracta, as well as in the other three legions of Radiolaria.

A. The "ciliary coronas" on the skeletal rods of dead Acanthometra were first described by the discoverer of this order, Johannes MÜller, and referred to as "the stumps of the contracted, thickened threads" (L. N. 12, p. 11, Taf. xi.).

B. The "number of the gelatinous cilia" I found constant in certain species of Acanthometra, and stated in my Monograph (L. N. 16, p. 115) "that here is to be found the first differentiation of the diffuse sarcode into definite organs of regular definite number, size, and position, which deserve the name tentacles rather than pseudopodia."

C. The nature of the myophriscs as fibrillÆ allied to muscles was first discovered by R. Hertwig, who described them as "structures of peculiar nature," under the name of "contractile threads," and pointed out in detail their histological and physiological peculiarities (L. N. 33, pp. 16-19, Taf. i.).

97. The Exoplasm of the Peripylea.—The extracapsular protoplasm of the Spumellaria or Peripylea is in communication with the intracapsular sarcode by the innumerable fine pores of the capsule-membrane, and like these pores is evenly distributed over the whole surface. The sarcomatrix which immediately surrounds the central capsule is moderately strong, and sends out innumerable long, thin pseudopodia, which probably correspond to the pores of the membrane. Their number is markedly greater in the Spumellaria than in the other three legions. The ramifications and communications which the radiating fibres of the sarcomatrix undergo within the calymma, apparently present the most manifold variations, so that the sarcoplegma or intracalymmar network thus formed has very diverse forms. On the surface of the calymma the exoplasmic threads constitute a variously disposed sarcodictyum, a regular or irregular exoplasmic network, by the silicification of which a primary lattice-shell arises in the majority of the Spumellaria. The free ends of the pseudopodia, which arise from this extracalymmar network and radiate out into the water, appear in most Spumellaria to be relatively short, but exceedingly numerous. Specially modified pseudopodia and axial threads in particular do not seem to occur in this legion. Perhaps, however, among the latter may be reckoned the remarkable pseudopodia which combine to form the sarcode flagellum in many Discoidea (and perhaps in other Spumellaria). This axoflagellum is a particularly strong thread of sarcode, arising from a definite point in the central capsule; it is cylindrical or slenderly conical in form, much longer, stronger, and more contractile than the ordinary pseudopodia; it contracts in a serpentine fashion on mechanical irritation and seems to originate by the fusion of a bundle of pseudopodia (compare § 95, C).

98. The Exoplasm of the Actipylea.—The extracapsular protoplasm of the Acantharia or Actipylea differs in several important respects from that of other Radiolaria, and appears to undergo more significant differentiations than that of the three other legions. Since the pores in the wall of the central capsule are not distributed evenly and at equal intervals over its whole surface (as in the Peripylea), but rather exhibit a regular disposition in groups at unequal intervals, the number of projecting pseudopodia is much less and the law of their arrangement different from that which obtains in the Peripylea (§ 58). In many and probably in all Acantharia they are divided into two groups, those which arise from the centre of the capsule and possess firm axial threads, and those which have not these characters (compare § 95, A). The axopodia, or stiff pseudopodia with axial threads, arise from the centre of the capsule, are present in much smaller numbers than the soft and flexible myxopodia, and are regularly disposed between the radial bars of acanthin, usually so that they are as far removed from them as possible, i.e., in the centre between each three or four bars; these latter may indeed be regarded as strongly developed axial threads, which have become changed into acanthin (§ 95, A). The soft myxopodia, or pseudopodia without axial threads, are much more numerous than the others, and arise from the sarcodictyum or exoplasmic network which ramifies over the surface of the calymma. Their number and arrangement seem, however, in many (if not in all) Acantharia to be regular and not to possess the extraordinary variability seen in the other three legions. In many Acanthometra the sarcodictyum exhibits a symmetrical conformation, with regular or subregular, polygonal (mostly hexagonal) meshes, and generally the stronger threads of the sarcodictyum secrete a firm, homogeneous or fibrillar, striated substance, which forms a network of ridges on the surface of the calymma. In the Acanthophracta the place of this is taken by the acanthin network of the primary lattice-shell. The axopodia of the Acanthometra are usually about as long as the radial spines between which they stand; their stiff axial thread is surrounded by a soft sheath of protoplasm, communicating with the thin sarcomatrix which surrounds the central capsule. Numerous branches pass into the calymma from the exoplasmic sheath of the axial threads, and form by their interweaving a loose sarcoplegma. The most peculiar differentiated products of the exoplasm of the Acantharia, however, are the myophane fibrillÆ of the Acanthometra, which have already been described under the name of myophriscs (§ 96).

102. The Chemical Peculiarities of the Skeleton.—The chemical composition of the skeleton shows very marked variations in the different legions of the Radiolaria. The two legions Spumellaria and Nassellaria (united formerly as "Polycystina") form their skeleton of pure silica (see note A, below); the legion PhÆodaria of a silicate of carbon (see note B), and the Acantharia of a peculiar organic substance—acanthin (see note C). This explains the well-known fact that the deposits of fossil Radiolaria (or Polycystine marls) are composed exclusively of the skeletons of Spumellaria and Nassellaria, those of the Acantharia and PhÆodaria being entirely absent (in the case of the last group, however, exception must be made in favour of the Dictyochida, or those PhÆodaria whose skeleton is made up of isolated scattered tangential siliceous fragments). The enormous deposits of Radiolarian skeletons in the deep sea of today, which constitute the Radiolarian ooze, consist, like the fossil Polycystine marls, almost exclusively of the shells of Spumellaria and Nassellaria, though here the acanthin skeletons of the Acantharia may be present in very small numbers, and the silicate skeletons of the PhÆodaria, which offer more resistance to the solvent action of sea-water, somewhat more abundantly. Calcareous skeletons do not occur in the Radiolaria (see note D).

A. The pure siliceous skeletons of the Polycystina were first recognised in 1833 by Ehrenberg in chalky marls (L. N. 2, p. 117). Since the two legions Acantharia and PhÆodaria were entirely unknown to Ehrenberg, his name Polycystina has reference only to the Spumellaria and Nassellaria.

B. The silicate skeleton of the PhÆodaria was formerly taken by me for a purely siliceous one. When I described the first PhÆodaria in my Monograph in 1862, I was only acquainted with five genera and seven species, whilst the number of PhÆodaria here described from the Challenger amounts to eighty-four genera and four hundred and sixty-five species. In the vast majority of these (though not in all) the skeleton becomes more or less intensely stained by carmine, and is also more or less charred at a red heat, in some even becoming of a blackish-brown. In many PhÆodaria, furthermore, the hollow skeletal tubes are destroyed by the continued action of heat. They are also, for the most part, strongly acted upon, or even destroyed by boiling caustic alkalis, whilst boiling mineral acids have no effect upon them. The best method of cleaning the skeletons of PhÆodaria from their soft parts is to heat them in concentrated sulphuric acid, and then add a drop of fuming nitric acid; in this they are not dissolved even on prolonged heating. From these facts it would appear that the skeletons of the PhÆodaria consist of a compound of organic substance and silica, or a "carbonic silicate." The more intimate composition yet remains to be discovered, as also the manifold differences which the various families of PhÆodaria seem to show in respect of its composition. The small skeletal fragments of the Dictyochida (the only remains of PhÆodaria which occur as fossils) appear to consist of pure silica.

C. The acanthin skeleton of the Acantharia was first described as such in my Monograph (1862, pp. 30-32). Johannes MÜller, the discoverer of this legion, took them for siliceous skeletons and defined the Acanthometra as "Radiolaria without lattice-shell, but with siliceous radial spines" (L. N. 12, p. 46). I formerly supposed that the acanthin skeletons in some of the Acantharia were partially or wholly metamorphosed into siliceous skeletons, but, according to the investigations of R. Hertwig, this does not appear to be the case; he showed that the skeletons of the most varied Acanthometra and Acanthophracta are completely dissolved under the longer or shorter action of acids, and supposes that in all Acantharia, without exception, the skeleton is composed of acanthin (1879, L. N. 33, p. 120). Quite recently Brandt has found that the acanthin spines dissolve not only in acids, alkalis, and "liquor conservativus" (as I had shown), but also in solutions of carbonate of soda (1 per cent.), and even of common salt (10 to 20 per cent.); he concludes from this that they consist of an albuminoid substance (vitellin) (L. N. 38, p. 400). I am unable to share this view, for I have never been able to see some of the most important reactions of albumen in any of the skeletons which I have examined, such for example as the xanthoproteic reaction, the red coloration with Millon's test, &c. They do not become yellow either with nitric acid or with iodine. In dilute mineral acids they dissolve more rapidly than in concentrated. My usual method of cleansing the skeleton of Acantharia (which has been practised with the same result on thousands of specimens) consists in heating the preparation in a small volume of concentrated sulphuric acid and then adding a drop of fuming nitric acid; all other constituents (the whole central capsule and the calymma) are thus very rapidly destroyed; the skeleton remains quite uninjured and withstands the combined action of the mineral acids for a longer or shorter time, though on prolonged heating it also is dissolved. I do not therefore regard acanthin as an albuminous substance, but as one related to chitin.

D. Calcareous skeletons have not been certainly demonstrated in the Radiolaria, and probably do not occur. Sir Wyville Thomson in his Atlantic (1877, L. N. 31, vol. i. p. 233, fig. 51) described under the name Calcaromma calcarea, a Radiolarian which contained scattered in its calymma numerous calcareous corpuscles "resembling the rowels of spurs." These are identical with the "toothed bodies, recalling crystal balls," which Johannes MÜller figured in the Mediterranean Thalassicolla morum so early as 1858, and compared with the "siliceous asterisks of Tethya" (L. N. 12, p. 28, Taf. vii. figs. 1, 2). I formerly regarded these peculiar calcareous corpuscles, whose solubility in mineral acids I had observed, as spicules of a Thalassicollid, and hence described the species in my Monograph as ThalassosphÆra morum (L. N. 16, p. 260). I have, however, seen reason to change my view, and am now led to suppose that those peculiar calcareous corpuscles, which may be named "Calcastrella," are not formed by the Radiolarian itself, but are foreign bodies which have been accidentally incorporated into the calymma of a Thalassicollid (Actissa). These corpuscles occur, often in large numbers, in many preparations in the Challenger collection, and in the calymma of other Radiolaria, chiefly Discoidea, hence it would appear that they are foreign bodies taken up by the pseudopodia and carried into the calymma by the circulation of the sarcode. The Radiolaria which Sir Wyville Thomson figured as Calcaromma calcarea, and MÜller as Thalassicolla morum, I regard as species of Actissa (see p. 13), perhaps Actissa radiata of the Pacific, and Actissa primordialis of the Mediterranean (compare the description of the ThalassosphÆrida of the Challenger collection, pp. 30, 31).

Upon this basis the first subdivision of the Radiolaria was made by Johannes MÜller, who recognised three groups:—"I. Thalassicolla, without receptacle, naked or with spicules; II. Polycystina, with a siliceous receptacle; III. Acanthometra, without receptacle, but with siliceous radial spines" (L. N. 12, p. 16).

106. The Ectolithia and Entolithia (Extracapsular and Intracapsular Skeletons).—The relation of the skeleton to the central capsule in the Radiolaria is very various in many respects; in the first instance two great groups, Ectolithia and Entolithia (see note A), may be distinguished topographically by mere external observation; in the former the skeleton lies entirely outside the central capsule; in the latter, partially at all events, within it. The Ectolithia, with a completely extracapsular skeleton, include all Nassellaria and PhÆodaria, as well as a great part of the Spumellaria (all Collodaria and the most archaic forms of SphÆrellaria); the Entolithia, on the other hand, in which the skeleton lies partly within, partly without the central capsule, include all Acantharia and the majority of the Spumellaria (most SphÆrellaria, see note B).

A. The difference between Ectolithia and Entolithia was applied in my Monograph in 1862 (p. 222) to separate the Monocyttaria into two main groups. The arrangement was, however, quite artificial, being contrary to the natural relations of the larger groups, as was shown seventeen years later by the discovery of the different structural relations of the central capsule.

107. Perigenous and Centrogenous Skeletons.—Much more important than the topographical relation of the skeleton to the central capsule, according to which the Ectolithia and Entolithia are separated from each other (§ 106), is the original development of the skeleton within or without the central capsule, which gives rise to the distinction between perigenous and centrogenous skeletons. Centrogenous skeletons are found only in the Acantharia, which are further distinguished from all other Radiolaria by their skeleton being formed of acanthin; in all Acantharia the formation of the skeleton begins in the middle of the central capsule, from which twenty (the number is inconstant only in the small group Actinelida) radial spines are centrifugally developed. The three other legions, on the contrary, possess on the whole a perigenous skeleton, which originally develops outside the central capsule and never in its middle. In the Nassellaria and PhÆodaria the skeleton retains this extracapsular position, as also in the Beloidea and part of the SphÆrellaria among the Spumellaria; in the great majority of the latter, however, the primary perigenous skeleton is subsequently enveloped by the growing central capsule, so that it lies partially within it (§ 109).

108. Polyphyletic Origin of the Skeleton.—The skeleton of the Radiolaria has undoubtedly originated polyphyletically, for it is impossible to derive its manifold varieties from a single ground-form, or to regard them as modifications of one type. It is much more probable that the different skeletonless Radiolaria have entered upon different ways of skeleton formation quite independently of each other. At the outset it is quite clear that the skeletons of the four legions have originated independently of each other. Further, it is certain that within the legion of the Spumellaria the Beloid skeletons of the Collodaria are not connected with the SphÆroid skeletons of the SphÆrellaria and the forms derived from them (see § 109). In the same way the skeletons of the PhÆodaria are polyphyletic; probably in this legion the Beloid, SphÆroid, Cyrtoid, and Conchoid skeletons have been developed quite independently (see § 112). In the Nassellaria, on the other hand, it is possible that all the skeletal forms are to be derived monophyletically from a single simple primitive form (either the sagittal ring or basal tripod?) (see § 111). Still more probable is it that the Acantharia have arisen monophyletically, for all the forms of their acanthin skeleton may be derived without violence from Actinelius (see § 110).

111. The Skeleton of the Nassellaria.—The skeletons of the Nassellaria or Monopylea consist of silica, and are never composed of separate portions, but constitute always a single continuous piece. The ground-form is originally monaxon, corresponding to that of the central capsule, with a constant difference between the two poles of the vertical main axis. The ground-form is never spherical or polyaxon as in the lattice-shells of the Spumellaria, and the skeleton never consists of hollow tubes, as in the PhÆodaria. The legion Nassellaria may be divided into two orders; in the Plectellaria (three suborders Nassoidea, Plectoidea, Stephoidea) the skeleton does not form a complete lattice-shell; in the Cyrtellaria, on the other hand, which are derived from these, the siliceous skeleton forms a complete lattice-shell enclosing the central capsule. The number of forms thus developed is astonishingly great, so that among the Nassellaria no less than two hundred and seventy-four genera and sixteen hundred and eighty-seven species may be distinguished, almost as many as in the SphÆrellaria. In spite of this great variety of forms the legion Monopylea is probably monophyletic; at least all the different skeletal forms may be derived from three elements which are combined in the most manifold fashion; (1) the sagittal ring, a simple siliceous ring, which lies vertically in the sagittal plane of the body, encircles the central capsule and comes into contact with it at the basal pole of the main axis (§ 124); (2) the basal or oral tripod, composed of three diverging radial spines, which meet in the middle of the basal pole of the central capsule (or in the centre of the porochora) (§ 125); (3) the cephalis, or lattice-head, a simple ovoid or subspherical lattice-shell, which encloses the central capsule and stands in connection with it at the basal pole of its main axis. Any one of these three important structural elements of the Nassellarian skeleton may possibly be the starting-point for all the remaining forms of the Monopylea; the great difficulty in their phylogenetic derivation lies in the facts that, on the one hand, any one of the three elements may alone constitute the skeleton, and on the other hand, in the great majority of the legion, two or three are united together (compare §§ 182-185).

113. Types of Skeletal Formation.—No less than twelve different principal forms may be distinguished as morphological types of the formation of the skeleton in the Radiolaria; some of these are peculiar to a single legion or even to a smaller group; but sometimes the same form occurs in several legions. Some types occur only in an isolated manner, independently of the others, but most exist in various combinations with other types. Of the twelve described below the Conchoid and Cannoid occur only in the PhÆodaria; the Plectoid and Circoid only in the Nassellaria; the Astroid only in the Acantharia; the remaining seven types are found in several legions in the same form and hence are polyphyletic.

116. The SphÆroid Skeletons or Lattice-Spheres.—The "lattice-spheres" or sphÆroid skeletons are the simplest and most primitive forms of lattice shells, and are widely distributed in the three legions Spumellaria, Acantharia, and PhÆodaria, whilst they are entirely wanting in the Nassellaria. The round lattice-shell is either a true sphere in the geometrical sense, or an endospherical polyhedron, i.e., a polyhedron, all whose angles lie in the surface of a sphere (§ 25). In general, primary and secondary lattice-spheres may be distinguished, of which the former are secreted on the outer surface of the primary, the latter on that of the secondary calymma (§ 85). Furthermore, simple and compound lattice-spheres may be distinguished, the latter of which consist of two or more concentric lattice-spheres firmly united by radial bars; in such cases the innermost lattice-sphere is always to be regarded as the oldest or primary, all the succeeding ones as secondary, and the outermost as the youngest (§ 129). The simple lattice-spheres are usually to be regarded as primary; they may, however, occasionally be secondary, in which case the primary shell, originally enclosed, has been lost by degeneration (as, for example, in the case of the AulosphÆrida and some SphÆrellaria).

121. The Discoid Skeletons or Lattice-Discs.—The "lattice-discs" or Discoid skeletons are characteristic of the Spumellarian group Discoidea, and have arisen from the lattice-spheres of the SphÆroidea by a less development of one axis, which is the main axis of the body, and is probably usually vertical; its two poles are always equal. The Discoid lattice-shell is either a biconvex lens (with a thin margin), or a plane disc (a shortened cylinder with thick margin), or some form intermediate between the two. All Discoid shells show a horizontal median plane or equatorial plane, by which they are divided into two equal halves, an upper and lower; the margin of the lens itself is originally the equator. The main axis, the shortest of all the axes of the shell, stands vertically in the centre of the equatorial plane. Among the PhÆodaria Discoid shells rarely occur (Aulophacus), as also among the Acantharia (Hexalaspida).

130. Dictyosis or Lattice Formation of the Skeleton.—In the great majority of Radiolaria the dictyosis or formation of lattice-work, and especially the formation of a variously-shaped "lattice-shell," plays such an important part that the whole class has long been popularly known in Germany by the name "lattice animalcules" ("Gitterthierchen" or "Gitterlinge") (Protista dictyota). The old name Polycystina also (1838), although referring only to the Spumellaria and Nassellaria, is derived from the lattice-work of the siliceous skeleton. The extremely various forms in which this is manifested furnish the means of distinguishing species. The specific conformation of the skeletal lattice-work is usually caused by the special disposition of the sarcodictyum (§ 94), whose exoplasmatic threads become silicified or (in the Acantharia) converted into bars of acanthin. In many cases, however, the form of the lattice is mainly dependent upon the situation and form of the radial spines or of special processes from them. With respect to their origin, two varieties of lattice may be distinguished—simultaneous and successive. Simultaneous dictyosis occurs especially in the simple lattice-shells of the SphÆrellaria and PhÆodaria, where, at a given moment ("dictyotic moment") the whole lattice of the shell is excreted on the surface of the calymma. Successive dictyosis, on the other hand, is found more particularly in the lattice-shells of the Acantharia (and in the concentric cortical shells of many SphÆrellaria), which develop from the separate lattice-plates formed by the apophyses of the radial spines, and hence not at the same moment. The lattice-shells of the Cyrtellaria, which gradually grow out from a sagittal ring or a basal tripod, arise by successive dictyosis.

135. Radial Spines of the Skeleton.—The skeleton in the great majority of Radiolaria is armed with radial spines, which are of great importance in the development of their general form and of their vital functions. From a morphological point of view the number, arrangement, and disposition of the spines is usually the determining factor as regards the general form of the skeleton. Physiologically they discharge distinct functions, as organs of protection and support; they act also, like the tentacles of the lower animals, as prehensile organs, since their points, lateral branches, barbed hooks, &c. serve to hold fast nutritive materials. In general main-spines and accessory spines may be distinguished in most Radiolaria; the former are of pre-eminent importance in determining the figure of the skeleton; the latter are merely appendicular organs. The main-spines present such characteristic and important differences in the various legions of Radiolaria that they must be considered separately.

137. Radial Spines of the Acantharia.—The radial spines of this legion have a much greater significance than in the other three classes of Radiolaria, since here alone they are the primary determining factors in the skeletal structure, and grow outwards from the middle of the central capsule. This centrogenous origin of the radial spines is as characteristic of the Acantharia as their chemical constitution, which is not siliceous but acanthinic (§ 102). Furthermore, their form is in most cases so peculiar that even an isolated Acantharian spine can be generally distinguished from one belonging to either of the other three legions. In the great majority of the Acantharia (all Acanthonida and Acanthophracta) twenty radial spines are constantly present, which, disposed according to a definite geometrical law, make up the skeleton (compare § 110 above and p. 717). The twenty spines are generally simply apposed to each other in the centre (either by the surfaces or the edges of their pyramidal base); more rarely they are completely united and form a single star-like piece of acanthin (Astrolithium). Very rarely (Acanthochiasma) each two opposite spines are united so that ten diametric bars cross in the middle of the central capsule. Whilst in the great majority of Acantharia these twenty radial spines are present, the small group Actinelida is characterised by the possession of an inconstant, often very large number, sometimes over one hundred. Among these Actinelida are probably to be found the stem-forms of the whole legion. The variously modified spines of the Acantharia may be grouped in three main categories: (1) round (cylindrical or conical); (2) four-edged (prismatic or pyramidal); (3) two-edged (leaf- or sword-shaped). The latter very commonly bear two opposite transverse processes, the former four crossed ones. By ramification and union of these apophyses arise the lattice-shells of the Acanthophracta (excepting the SphÆrocapsida).

The skeletons of the Radiolaria, in addition to the general relations which have been discussed above, present numerous and important special differences in the various larger and smaller groups. These are indicated in detail in the descriptions of the legions, orders, and families in the systematic portion of this Report.

BIOGENETICAL SECTION.

A SKETCH OF OUR KNOWLEDGE OF THE DEVELOPMENT OF THE RADIOLARIA IN THE YEAR 1884.

Chapter V.—ONTOGENY OR INDIVIDUAL DEVELOPMENT.

(§§ 141-152.)

141. Individual Developmental Stages.—The germinal history of the Radiolaria presents great obstacles to direct observation, and hence is very incompletely known. The fragmentary observations, however (having been made on Radiolaria of very various groups and supplemented by comparative anatomical considerations), allow us to draw a general picture of the essential developmental processes in this great class. It may probably be assumed that in all Radiolaria, after maturation, the central capsule discharges the function of a sporangium, and its contents are broken up into numerous flagellate swarm-spores (zoospores). After these flagellate swarm-spores (resembling Astasia) have emerged from the ruptured central capsule, they probably pass over into a Heliozoan-stage (Actinophrys) and then after the formation of a jelly-veil into the condition of SphÆrastrum. Afterwards, when a membrane is formed between the outer jelly-veil and the inner nucleated cell-body, an Actissa-stage arises, which exhibits in its simplest form the differentiation of the spherical unicellular body into the central capsule and calymma. Actissa thus represents both ontogenetically and phylogenetically the primitive condition of the Radiolarian organism, and may thus be regarded as the point of departure of all other forms.

A. The formation of the motile spores in the central capsule was first observed by J. MÜller in Acanthometra (1856, L. N. 10, p. 502), then by A. Schneider in Thalassicolla (1858, L. N. 13, p. 41), and finally by myself in SphÆrozoum (1859, L. N. 16, p. 141). These older observations were, however, incomplete, for the origin of the motile corpuscles from the contents of the central capsule was not observed. The first complete and detailed observations upon the formation of spores in the Radiolaria were published in 1871 by Cienkowski (L. N. 22, p. 372, Taf. xxix.); they relate to two different Polycyttaria, CollosphÆra and Collozoum. These investigations were supplemented by R. Hertwig on Collozoum and Thalassicolla (1876, L. N. 26, pp. 28, 43, &c.); on Collozoum he made the important discovery that the Polycyttaria form two kinds of spores, one with and the other without crystals, and that the latter are divided into macrospores and microspores (compare the chapter on "Reproduction," §§ 212-216). Quite recently Karl Brandt has confirmed these observations, and has extended them to all the genera of Polycyttaria (1881, L. N. 38, p. 393, and 1885, loc. cit.).

B. The number of flagella, projecting from each spore, is very difficult to determine, owing to their extraordinary length and slenderness. It appeared to me that in the majority of those Radiolaria whose spores I investigated only a single flagellum could be demonstrated with certainty, although sometimes two, springing from a common base, seemed to be present. Compare the chapter on "Reproduction," (§ 215) and the recent work of Karl Brandt on SphÆrozoea (1885, L. N. 52, pp. 145-174).

143. The Actinophrys-Stage.—The fate of the flagellate zoospores which emerge from the mature central capsule of the Radiolaria has not hitherto been decided by actual observation; all attempts to rear the swarming zoospores have been in vain, for they have soon died. From what we know, however, of the comparative morphology of the Protista, the hypothesis is fully justified, that between the Astasia-stage of the flagellate swarm-spores, and the well-known Actissa-stage of the simplest Radiolaria, there lies an intermediate developmental stage, which may be regarded as being essentially the simplest Heliozoan form, Actinophrys or Heterophrys. The swarm-spore is very probably converted directly in to a simple floating Heliozoon by its elongated or ovoid body becoming spherical and by fine pseudopodia protruding all round instead of a single flagellum; the nucleus at the same time assuming a central position.

144. The SphÆrastrum-Stage.—The Actinophrys-stage of the young Radiolaria, which proceeds immediately from the flagellate zoospore, is probably connected with the Actissa-stage by an intermediate form, which may be regarded as a simple skeletonless Heliozoon with a jelly-veil; a well-known example of such a form is SphÆrastrum (in the solitary, not the social condition) and Heterophrys. This important intermediate form has arisen from the simple Actinophrys-stage by the excretion of an external structureless jelly-veil, such as is formed in many other Protista (e.g., in the encystation of many Infusoria). The young Radiolarian in this second Heliozoon-stage becomes a simple cell with pseudopodia radiating on all sides; its body consists of three concentric spheres, the central nucleus, the protoplasmic body proper, and the surrounding calymma or jelly-veil. When a firm membrane is developed between the last two spheres this SphÆrastrum-stage passes over into the Actissa.

The gap in our empirical knowledge which still exists between the flagellate stage (§ 142) and the simplest Radiolarian stage (Actissa, § 145), can be filled hypothetically only by the assumption of several Heliozoon-stages following one upon another. It is possible also that the capsule-membrane is not formed between the endoplasm and exoplasm (as here supposed), but that the membrane was formed first outside the cell and the extracapsulum subsequently secreted around it.

145. The Actissa-Stage.—The first Spumellarian genus, Actissa, is not only the simplest form actually observed among the Radiolaria, and the true prototype of the whole class, but also the simplest form under which the Radiolarian organisation can be conceived. It is therefore extremely probably that Actissa not only forms the common stem-form of the whole class in a phylogenetic sense, but is also its common ontogenetic or germinal form. Probably in all Radiolaria the SphÆrastrum-stage develops immediately into the typical Actissa-stage, by the formation of a firm membrane between the protoplasmic body of the spherical Heliozoan cell and its jelly-veil. Thus arises the characteristic central capsule, which is wanting in the nearly related Heliozoa. It is further probable that all Radiolaria in their early stage will so far conform to the state of things in Actissa as to have the capsule-membrane of the spherical skeletonless cell perforated everywhere by fine pores. This structure is retained in all Spumellaria, whilst in the other three legions those structural relations of the capsule which are characteristic of each develop from the Actissa-stage.

146. The Ontogeny of the Spumellaria.—In the simplest case the individual development in the Spumellaria ceases with the Actissa-stage. In all other genera of this legion diverging forms proceed from this, of which the different growth of the three dimensive axes on the one hand (§§ 44, 45), and the differentiation of the various parts of the unicellular organism with the formation of the skeleton on the other, are of pre-eminent significance. Even in the varying growth of the central capsule in the different dimensions of space in the skeletonless Colloidea, four different modes may be distinguished, which further, in the corresponding development of the skeleton, furnish the basis for the origin of the four orders of SphÆrellaria. The most primitive and simplest form of growth, equal extension in all directions, is found in the spherical central capsule and the concentric spherical skeletons (Procyttarium, SphÆroidea). When the growth of the central capsule proceeds more rapidly in the direction of the vertical main axis than in any other direction, the ellipsoidal or cylindrical central capsule (Actiprunum) arises, and the vertically elongated skeleton of the Prunoidea, which is derived from it. When, on the contrary, the growth of the central capsule and lattice-shell is less in the direction of the vertical main axis than in any other direction, the lenticular or discoid central capsule (Actidiscus) arises, and the corresponding lenticular shell of the Discoidea. Finally, even quite early in many Spumellaria, the growth of the central capsule and of the corresponding lattice-shell in the three dimensive axes is different, and hence arise the lentelliptical forms whose geometrical type is the triaxial ellipsoid or the rhombic octahedron (Actilarcus, Larcoidea). Thus the origin of the four orders of SphÆrellaria is simply explained by a varying growth in the different dimensive axes. The primary (innermost) lattice-shell is in this legion always simultaneously developed (suddenly excreted at the moment of lorication from the sarcodictyum). The secondary lattice-shells, on the other hand, which surround the former concentrically, and are united with it by radial bars, arise successively from within outwards.

147. The Ontogeny of the Acantharia.—The individual development of the Acantharia in the simplest case (Actinelius) stops at a point which differs from the Actissa-stage only in the change of radial axial threads into acanthin spines. In the small group Actinelida, their number remains variable and usually indeterminate (Adelacantha), whilst in the great majority of the legion (Acanthonida and Acanthophracta) the number is constantly twenty, and those spines are regularly arranged according to the MÜllerian law in five parallel circles, each containing four crossed spines (Icosacantha). The simplest form among these latter is Acanthometron, which may be regarded both ontogenetically and phylogenetically as the common starting-point of all the Icosacantha. Within this extensive group variations in the length of the dimensive axes appear, similar to those observed in the Spumellaria. In the Astrolonchida and SphÆrophracta the central capsule remains spherical, extending equally in all directions; and correspondingly the lattice-shell, which is excreted on the surface of the spherical calymma, remains spherical. In the Belonaspida (just as in the Prunoidea) this form passes over into an ellipsoid by prolongation of one axis; on the contrary, in the Hexalaspida (as in the Discoidea) the discoidal or lenticular form arises by shortening of an axis. Finally, in the Diploconida, and in some Hexalaspida in which the growth is different in all three dimensive axes (as in the Larcoidea), both the central capsule and the shell assume the lentelliptical form. The lattice-shell of the Acanthophracta is usually successive in its development, since from each of the twenty radial spines two or four tangential apophyses proceed, whose branches subsequently unite and combine to form the lattice-shell. Only in the peculiar SphÆrocapsida can the pavement-like shell arise simultaneously or in a moment of lorication.

148. The Ontogeny of the Nassellaria.—The individual development of the Nassellaria in the simplest instance remains stationary at the skeletonless Nasselid stage (Cystidium, Nassella), which can be immediately derived from the foregoing Actissa-stage by the disappearance of the pores in the upper (apical) hemisphere of the central capsule, whilst in the lower (basal) portion they are modified to form a porochora; the podoconus is developed within the endoplasm upon this latter. Usually the spherical form of the central capsule passes over into an ovoid or ellipsoidal one, the vertical axis which passes through the centre of the porochora being elongated. From the skeletonless Nassellida the other Nassellaria may be derived both ontogenetically and phylogenetically by the excretion of an extracapsular siliceous skeleton. Unfortunately, the earliest stages in the formation of this skeleton are unknown, and hence no answer can at present be given to the important question, in what order the three primary skeletal elements of the Nassellaria (the basal tripod, sagittal ring, and latticed cephalis) appear (compare §§ 111 and 182). If, for example, in Cortina and Tripospyris the basal tripod were to appear first in the ontogeny, and the sagittal ring were developed from this, then the Plectoidea would be rightly considered to be the oldest forms in the phylogeny of the skeleton-forming Nassellaria; and in the contrary case the Stephoidea would be so regarded. The relations of growth in the three dimensive axes are very variable in the Nassellaria; the three most important factors in this respect (partly separately and partly in combination) are; (1) the development of the basal tripod to a triradial stauraxon form (the ground-form being a three-sided pyramid); (2) the development of the sagittal ring in the median plane of the body (the vertical axis having the poles different); (3) the development of the latticed cephalis outside the central capsule (the poles of the vertical axis being again different). Since the development both of the skeleton and of the malacoma is characterised in most Nassellaria by the stronger growth of the vertical axis and the differentiation of the two poles, the allopolar monaxon ground-form acquires a predominant significance in this legion (§ 32); the starting point of most of the further modifications is the basal pole of the vertical main axis. Next to this the sagittal axis is usually the most important determining factor (its dorsal and ventral poles being usually different), more rarely the frontal axis (with equal right and left poles). In the zygothalamous Spyroidea (as in the Stephoidea) the formation of the shell proceeds from the sagittal ring, whilst in the polythalamous Cyrtoidea the latticed cephalis is always the starting point, from which a series of joints (thorax, abdomen, and in the Stichocyrtida, the numerous post-abdominal joints) successively arise (unipolar growth).

149. The Ontogeny of the PhÆodaria.—The individual development of the PhÆodaria in the simplest case stops with the skeletonless condition of the PhÆodinida (PhÆodina, PhÆocolla), which can be immediately derived from the foregoing Actissa-stage by the disappearance of the pores in the greater part of the central capsule, the characteristic astropyle being developed at the basal pole (§ 60). Since this particular form and structure of the spheroidal central capsule remains the same in all PhÆodaria, whilst the formation of their skeleton follows very different directions, it follows that further common paths of development are excluded both ontogenetically and phylogenetically. What will be laid down in this respect as regards the phylogeny of the different groups of PhÆodaria (§§ 194-199) holds true also of their ontogeny. The relations of growth in the three dimensive axes are hence very different in the skeletons of the various groups of PhÆodaria. This difference is best marked in the PhÆoconchia, whose bivalved lattice-shells have as their ground-form the rhomboid pyramid of Ctenophora. In most PhÆogromia the monaxon lattice-shell may develop simultaneously by sudden excretion at a particular moment of lorication; this is also the case with the polyaxon lattice-shells of the PhÆosphÆria. In their future growth the development of basal or radial apophyses is of special importance. In the majority of the PhÆodaria these apophyses are tubes of silicate filled with jelly (often provided with an axial siliceous thread); thus their development is distinguished by complications which are absent in the case of the other three legions.

150. Growth.—The growth of the body in the Radiolaria, as in all other organisms, is the fundamental function of individual development (see note A). All structural relations which this richest class of the Protista exhibits may be referred to different forms of growth, either of the unicellular malacoma or of the skeleton which it produces. In general the special development of the skeleton is dependent upon that of the central capsule, and of the sarcodictyum on the surface of the calymma; in the further growth, however, the conditions are reversed, and the condition of the skeleton already formed directly determines the further development of the central capsule and of the calymma with its sarcodictyum. The four legions of Radiolaria show, speaking generally, certain characteristic differences in growth, which are due in great part to the different structure and ground-form of their central capsule. In the two legions of the Porulosa (Spumellaria and Acantharia), in which the central capsule is originally spherical and the ground-form of the skeleton either polyaxon or isopolar monaxon, two fundamental and variously combined directions of growth are recognisable; firstly, the concentric growth (equal increase of volume in all directions), and secondly, multipolar or diametral growth (hypertrophy of certain parts in the direction of definite pairs of radii). A different state of things obtains, however, for the most part, in the two legions of the Osculosa (Nassellaria and PhÆodaria), in which the central capsule possesses a vertical main axis with different poles, and the structure of the skeleton is determined by this allopolar monaxon ground-form. The two fundamental directions of growth here combined in the most various ways are, firstly, unipolar growth (starting from the basal pole of the vertical main axis), and secondly, radial or pyramidal growth (characterised by the different development of separate parts in the direction of definite radii). Whilst the growth of the malacoma is dependent on intussusception (as in most organic structures capable of imbibing), the growth of the skeleton in all Radiolaria takes place by apposition (see note B).

A. The earliest investigations into the modes of growth in the Radiolaria are due to J. MÜller (L. N. 12, pp. 21-33). More detailed communications I gave myself in my Monograph (L. N. 16, pp. 150-159). The relations there sketched have now, in consequence of the examination of the Challenger collection, undergone many important additions, and in some divisions, important modifications; these are for the most part treated of in the general account of the separate families.

B. The view here maintained, that the skeleton of all Radiolaria grows only by apposition, appeared formerly to have certain exceptions. I thought I had shown that in Coelodendrum the thin-walled tubes grew not only in length but also in thickness, with continuous increase in the lumen (L. N. 16, pp. 152, 360). Further K. Brandt concluded, from the varying size of the median bars in the twin-spicules of SphÆrozoum, that these siliceous structures grow by intussusception (L. N. 38, p. 401). Both suppositions have been proved erroneous and I have come to the opinion that in all Radiolaria the skeleton grows by apposition.

151. Regeneration.—Whilst the general course of individual development (perhaps without any exception in the Radiolaria), begins with the formation of zoospores in the central capsule, there yet occurs in some groups a different form of ontogeny, introduced by simple division of the unicellular organism, and coming under the term "regeneration" in its wider sense. This spontaneous division occurs quite commonly in the Polycyttaria (or social Spumellaria), and produces their colonies (compare the chapter on Reproduction, § 213). On the contrary, it has not been observed in the solitary Spumellaria, nor in the Acantharia and Nassellaria; possibly, however, the peculiar Acantharian family, Litholophida, has arisen by the division of Acanthonida (compare p. 734). Among the PhÆodaria division is commonly observed in the order PhÆocystina (which have an incomplete Beloid skeleton or none), and also in the PhÆoconchia. In all these cases the increase by division is nothing else than an ordinary case of cell-division, in which bisection of the nucleus precedes that of the central capsule. The regeneration by which each of the two daughter-cells develops to a complete mother-cell depends upon simple growth. Another form of regeneration, different from this, has been observed in Thalassicolla. If the central capsule be extracted artificially from the large concentric calymma, the enucleated central capsule produces a new extracapsulum, with sarcomatrix, pseudopodia, and calymma. This experiment may be repeated several times with the same result. (Compare A. Schneider, 1867, L. N. 20.)

153. Sources of Phylogenetic Knowledge.—For the purpose of constructing a hypothetical genealogical tree of the Radiolaria, as of all other organisms, three sources of information are open to us, viz., palÆontology, comparative ontogeny, and comparative anatomy. In the present case, however, these three sources are of very different value; the first two are at present only very inadequately known and have only been partially investigated, hence they can only be utilised to a very slight extent. The comparative anatomy of the Radiolaria, on the other hand, is so completely known, and affords such certain glimpses into the morphological relations of the related groups, that by its aid we are in a position at all events to lay down the general features of their phylogeny with some probability, and to lay the foundation of a natural system.

154. Natural and Artificial Systems.—Although in the classification of the Radiolaria, as in the case of all other organisms, the natural system must be regarded as the goal of systematic classification, our phylogenetic knowledge of the Radiolaria is too fragmentary and inadequate to admit of the systematic arrangement here adopted being regarded as a thoroughly consistent natural system, that is, as representing the true genealogical tree of the class. Owing, however, to the extraordinary variety of form of the Radiolaria, and the complicated relationships of the larger and smaller groups, a synoptical grouping of the different categories and the erection of a complete, even if to some extent artificial, system, becomes a logical necessity. Under these circumstances, and regard being had to both these conditions, the following systematic treatment of the Radiolaria will appear as a compromise between the natural and artificial systems, like all other zoological and botanical classificatory attempts. On the one hand, the attempt is made to arrange the larger and smaller groups as nearly as possible according to their phylogenetic relationships, whilst, on the other hand, the practice of circumscribing each by a definition as clear and logical as possible has been carried out. Since these two efforts naturally often come into contact, the insufficiency of many parts of the arrangement is obvious, hence its hypothetical and provisional character is emphatically stated.

155. Systematic Categories.—The categories or different orders of divisions have in the Radiolaria, as in all other organisms, no absolute significance, but only a relative value. In itself it is quite unimportant whether the whole group be regarded, as at first, as a family (Ehrenberg, 1847), or as an order (J. MÜller, 1858), or as a class (Haeckel, 1881). These different views are regulated, on the one hand, by the known extent of the group and by the amount of our acquaintance with it, and on the other, by comparison with related groups and by reference to their conventional disposition. When, therefore, the whole class, Radiolaria, is here divided into two subclasses, four legions, eight orders, eighty-five families, &c., these artificial categories are drawn up only in the conviction that by this means the easiest survey and most thorough insight into the system as a whole may be attained; this latter will indeed approach as far as possible the ideal of a natural system, but must on numerous practical grounds always remain more or less artificial. Since it is to be expected that with the progress of our systematic knowledge the rank of the various categories will rise, it is possible that in the future the arrangement of the group may be somewhat as follows:—Phylum, RADIOLARIA; Four Classes, Spumellaria, Nassellaria, Acantharia, PhÆodaria; Eight Legions (Nos. I.-VIII. in the following Table); Twenty Orders (Nos. 1-20 in the Table), &c.

Four Legions. Eight Sublegions. Twenty Orders. Typical Families.
I. Legion (or Subclass)
Spumellaria
(Peripylea)

[Porulosa peripylea.]		 brace I. Collodaria
(Spumellaria palliata)		 brace 1. Colloidea, brace 1a. Thalassicollida.
1b. Collozoida.
2. Beloidea, brace 2a. ThalassosphÆrida.
2b. SphÆrozoida.
II. SphÆrellaria
(Spumellaria loricata)		 brace 3. SphÆroidea, brace 3a. EthmosphÆrida.
3b. CollosphÆrida.
4. Prunoidea, brace 4a. Ellipsida.
4b. Zygartida.
5. Discoidea, brace 5a. Phacodiscida.
5b. Porodiscida.
6. Larcoidea, brace 6a. Larnacida.
6b. Pylonida.
II. Legion (or Subclass)
Acantharia
(Cannopylea).

[Osculosa cannopylea.]		 brace III. Acanthometra
(Acantharia palliata)		 brace 7. Actinelida, brace 7a. Astrolophida.
7b. Litholophida.
7c. Chiastolida.
8. Acanthonida, brace 8a. Astrolonchida.
8b. Quadrilonchida.
8c. Amphilonchida.
IV. Acanthophracta
(Acantharia loricata)		 brace 9. SphÆrophracta, brace 9a. SphÆrocapsida.
9b. Dorataspida.
9c. Phractopeltida.
10. Prunophracta, brace 10a. Belonaspida.
10b. Hexalaspida.
10c. Diploconida.

III. Legion (or Subclass)
Nassellaria
(Monopylea)

[Osculosa monopylea.]

 brace V. Plectellaria
(Nassellaria palliata)		 brace 11. Nassoidea, 11. Nassellida.
12. Plectoidea, brace 12a. Plagonida.
12b. Plectanida.
13. Stephoidea, brace 13a. Stephanida.
13b. Tympanida.
VI. Cyrtellaria
(Nassellaria loricata)		 brace 14. Spyroidea, brace 14a. Zygospyrida.
14b. Androspyrida.
15. Botryodea, brace 15a. Cannobotryida.
15b. Lithobotryida.
15c. Pylobotryida.
16. Cyrtoidea, brace 16a. Monocyrtida.
16b. Dicyrtida.
16c. Tricyrtida.
16d. Stichocyrtida.
IV. Legion (or Subclass)
PhÆodaria
(Actipylea)
[Porulosa actipylea.]		 brace VII. PhÆocystina
(PhÆodaria palliata)		 brace 17. PhÆocystina, brace 17a. PhÆodinida.
17b. Cannorrhaphida.
17c. Aulacanthida.
18. PhÆosphÆria, brace 18a. OrosphÆrida.
18b. AulosphÆrida.
18c. CannosphÆrida.
VIII. PhÆocoscina
(PhÆodaria loricata)		 brace 19. PhÆogromia, brace 19a. Challengerida.
19b. Castanellida.
19c. Circoporida.
20. PhÆoconchia, brace 20a. Concharida.
20b. Coelodendrida.
20c. Coelographida.
Four Legions.
Eight Sublegions.
Twenty Orders.
Typical Families.

I. Legion (or Subclass) (Peripylea)

[Porulosa peripylea.]
I. Collodaria (Spumellaria palliata)
1. Colloidea,
1a. Thalassicollida.
1b. Collozoida.
2. Beloidea,
2a. ThalassosphÆrida.
2b. SphÆrozoida.
II. SphÆrellaria (Spumellaria loricata)
3. SphÆroidea,
3a. EthmosphÆrida.
3b. CollosphÆrida.
4. Prunoidea,
4a. Ellipsida.
4b. Zygartida.
5. Discoidea,
5a. Phacodiscida.
5b. Porodiscida.
6. Larcoidea,
6a. Larnacida.
6b. Pylonida.

II. Legion (or Subclass) Acantharia (Cannopylea).

[Osculosa cannopylea.]
III. Acanthometra (Acantharia palliata)
7. Actinelida,
7a. Astrolophida.
7b. Litholophida.
7c. Chiastolida.
8. Acanthonida,
8a. Astrolonchida.
8b. Quadrilonchida.
8c. Amphilonchida.
IV. Acanthophracta (Acantharia loricata)
9. SphÆrophracta,
9a. SphÆrocapsida.
9b. Dorataspida.
9c. Phractopeltida.
10. Prunophracta,
10a. Belonaspida.
10b. Hexalaspida.
10c. Diploconida.

III. Legion (or Subclass) Nassellaria (Monopylea)

[Osculosa monopylea.]
V. Plectellaria (Nassellaria palliata)
11. Nassoidea,
11. Nassellida.
12. Plectoidea,
12a. Plagonida.
12b. Plectanida.
13. Stephoidea,
13a. Stephanida.
13b. Tympanida.
VI. Cyrtellaria (Nassellaria loricata)
14. Spyroidea,
14a. Zygospyrida.
14b. Androspyrida.
15. Botryodea,
15a. Cannobotryida.
15b. Lithobotryida.
15c. Pylobotryida.
16. Cyrtoidea,
16a. Monocyrtida.
16b. Dicyrtida.
16c. Tricyrtida.
16d. Stichocyrtida.

IV. Legion (or Subclass) PhÆodaria (Actipylea)

[Porulosa actipylea.]
VII. PhÆocystina (PhÆodaria palliata)
17. PhÆocystina,
17a. PhÆodinida.
17b. Cannorrhaphida.
17c. Aulacanthida.
18. PhÆosphÆria,
18a. OrosphÆrida.
18b. AulosphÆrida.
18c. CannosphÆrida.
VIII. PhÆocoscina (PhÆodaria loricata)
19. PhÆogromia,
19a. Challengerida.
19b. Castanellida.
19c. Circoporida.
20. PhÆoconchia,
20a. Concharida.
20b. Coelodendrida.
20c. Coelographida.

156. Formation of Species.—The totality of similar forms, which we unite in one species, and which in the earlier dogmatic systems was regarded as a category of absolute value, possesses only a relative value like all other systematic categories (§ 155). According to the individual views of the systematist and the general survey which he has attained of the smaller and larger systematic groups, the conception of a species adopted in his practical work will be wider or narrower. In the present systematic arrangement a medium extent has been adopted. It is shown that in the Radiolaria, as in all other extensive groups of organisms, the constancy of the species is very variable in the different groups. Many families of Radiolaria are very rich in "bad species," i.e., very variable forms, in which the process of the formation of species is seen in progress; such, for example, are—among the Spumellaria, the SphÆrozoida, StylosphÆrida, Phacodiscida and Pylonida; among the Acantharia, the Amphilonchida and Phractopeltida; among the Nassellaria, the Stephoidea and Botryodea; and among the PhÆodaria, the Aulacanthida, SagosphÆrida, Castanellida and Concharida. On the other hand, in some families numerous "good species" may be distinguished, since the intermediate connecting forms are no longer present and the forms have become relatively constant. As instances of such families may be mentioned, among the Spumellaria, the AstrosphÆrida, Cyphinida, Porodiscida and Tholonida; among the Acantharia the Quadrilonchida and Dorataspida; among the Nassellaria, the Spyroidea and Cyrtoidea; among the PhÆodaria, the Challengerida, Medusettida, Circoporida and Coelographida. The more carefully the different groups are studied, the more numerous the individuals of each species under comparison, the greater becomes the number of "bad" species among the Radiolaria, and the smaller the number of good ones. Originally, no doubt, all "species bonÆ" were "malÆ." There may be observed in the manifold skeletal forms of the Radiolaria, on the one hand, the utmost accuracy of configuration, and on the other, the greatest variability, and hence a careful comparative study of them leads to a firm conviction of the gradual "Transformation of Species," and of the truth of the "Theory of Descent."

157. PalÆontological Development.—The palÆontology of the Radiolaria already offers very considerable material for study; but in consequence of its incompleteness this is of little value for the study of the phylogeny of the class. By far the larger portion of the fossil Radiolaria belong to the Tertiary period; only quite recently have numerous well-preserved fossil Radiolaria been described from the Mesozoic period, and especially from the Jura. Of PalÆozoic Radiolaria (from the coal measures) only slight traces are known. Moreover, the fossil Radiolaria hitherto known have been found only in very circumscribed and widely separated localities. The majority of all the species belong to the small island of Barbados. Although our palÆontological acquaintance with the Radiolaria must necessarily be incomplete for this reason, it is still more so since at least thirty out of the eighty-five families (that is more than a third) could not possibly leave any fossil remains, either because they possess no skeleton, or because of its chemical composition.

Of the four legions of the Radiolaria, the Acantharia (on account of the solubility of their astroid acanthin skeletons) have entirely vanished and have never been found fossil. Of the PhÆodaria, whose silicate skeleton is not as a rule capable of fossilisation, only one section (Dictyochida) of a single family (Cannorrhaphida) has been observed fossil. Hence the fossil remains of the Radiolaria belong almost exclusively to the two legions, Spumellaria and Nassellaria, which were formerly united under the term "Polycystina." Among these, however, the skeletonless Thalassicollida, Collozoida, and Nassellida could leave no traces. Hence there only remain fifty-five families of which we might expect to find fossil siliceous skeletons. Even of these, however, scarcely the half are certainly known in the fossil condition, whilst of the remainder nothing certain is known; for example, of the large order Larcoidea (among the Spumellaria) and of the Stephoidea (among the Nassellaria) with a few isolated exceptions, no fossils are known. The great majority of fossil Radiolaria belong to the two Nassellarian orders Cyrtoidea and Spyroidea (two relatively very highly developed groups); next to these follow the orders Discoidea and SphÆroidea among the Spumellaria. From these palÆontological facts it is obvious that our present very incomplete acquaintance with the fossil Radiolaria is quite insufficient to warrant us in drawing any conclusions from it regarding the phylogenetic development or palÆontological succession of the individual groups.

158. Origin of the Four Legions.—The agreement of all Radiolaria in those constant and essential characters of the unicellular body, which distinguish them from all other Protista (especially the differentiation of the malacoma into a central capsule and extracapsulum), justifies the conclusion that all members of this class have been developed from a common undifferentiated stem-form. Only the simplest form of the Spumellaria, a skeletonless spherical cell with concentric spherical nucleus and calymma, can be regarded as such. The simplest form of the Thalassicollida which is now extant (Actissa, Procyttarium, p. 12), corresponds so exactly to the morphological idea of that hypothetical stem-form that it may unhesitatingly be regarded in a natural system as the common point of origin of the whole class. On the other hand, Actissa is so closely related to the simple Heliozoa (Actinophrys, ActinosphÆrium, Heterophrys, SphÆrastrum, &c.) that its origin from this group of Rhizopoda is exceedingly probable. The three legions Acantharia, Nassellaria, and PhÆodaria are to be regarded as three main diverging branches of the genealogical tree, which have been developed in different directions and are only connected by their simplest stem-forms (Actinelius, Nassella, PhÆodina) with the stem-form of the Spumellaria, the primordial Actissa.

159. Phylogeny of the Spumellaria.—The legion Spumellaria or Peripylea is to be regarded as the common stem-group of the Radiolaria, and its simplest form, Actissa, as the primitive genus or radical form of the whole class; for it possesses in the simplest and most undifferentiated form all those characters by which the Radiolaria are distinguished from other Protista; all the other genera of the class may be derived from it by successive modifications. Considered as a legion the whole group Spumellaria is undoubtedly monophyletic, for all its members possess those essential characters by which it is distinctively marked off from the other three legions, more especially a simple capsule-membrane, which is everywhere evenly perforated by innumerable small pores; the nucleus lies originally in the centre of the spherical central capsule. Furthermore, all Spumellaria lack those positive characters which distinguish the three remaining legions—the centrogenous acanthin skeleton of the Acantharia, the basal porochora and the monaxon podoconus of the Nassellaria, the astropyle and phÆodium of the PhÆodaria.

161. Hypothetical Genealogical Tree of the Spumellaria:—

Larcoidea
brace		 Discoidea
brace
Streblonida Phacodiscaria
Tholonida Coccodiscida
Prunoidea
brace		 Soreumida
Zygartida
Zonarida
Lithelida SphÆroidea Cyclodiscaria
brace Spongodiscida
StylosphÆrida Pylodiscida
Phorticida
Panartida
Artiscida
Phacodiscida
Spongodruppida
StaurosphÆrida
Spongel-
lipsida		 Pylonida
 
Cyphinida  
Porodiscida
AstrosphÆrida
Larnacida
CubosphÆrida Cenodiscida
Druppulida
CollosphÆrida Archidiscida
  Larnacilla
(Trizonium)
Spongurida
 
 
Ellipsida
(Cenellipsis)		 Larcarida
(Cenolarcus)		 LiosphÆrida
(CenosphÆra)		 Cenodiscida
(Cenodiscus)
 
[Actiprunum?] [Actilarcus?] [Procyttarium] [Actidiscus?]
 
 
CenosphÆra (Common stem-form of all SphÆrellaria?)
 
Polycyttaria
brace
CollosphÆrida Collozoida SphÆrozoida brace Beloidea
 
 
ThalassosphÆrida
EthmosphÆrida
 
 
Colloidea
 
Thalassicollida
 
Actissa
                                                                                                                       
Larcoidea
brace
Streblonida
Tholonida
Prunoidea
brace		 Soreumida
Zygartida
Zonarida
Lithelida
 
Phorticida
Panartida
Artiscida
 
Spongodruppida
 
Spongel-
lipsida		 Pylonida
 
Cyphinida
 
 
Larnacida
 
Druppulida
 
  Larnacilla
(Trizonium)
Spongurida
 
 
Ellipsida
(Cenellipsis)		 Larcarida
(Cenolarcus)
 
[Actiprunum?] [Actilarcus?]
 
≈ ≈
 
 
Discoidea
brace
Phacodiscaria
Coccodiscida
 
SphÆroidea Cyclodiscaria
brace Spongodiscida
StylosphÆrida Pylodiscida
 
Phacodiscida
 
StaurosphÆrida
 
 
Porodiscida
AstrosphÆrida
 
CubosphÆrida Cenodiscida
 
CollosphÆrida Archidiscida
 
≈  
LiosphÆrida
(CenosphÆra)		 Cenodiscida
(Cenodiscus)
Actiprunum
Actilarcus		  
[Procyttarium] [Actidiscus?]
 
 
CenosphÆra (Common stem-form of all SphÆrellaria?)
 
Polycyttaria
brace
CollosphÆrida Collozoida SphÆrozoida brace Beloidea
 
 
ThalassosphÆrida
EthmosphÆrida
 
 
Colloidea
 
Thalassicollida
 
Actissa

162. Collodaria and SphÆrellaria.—Whilst in all Spumellaria the malacoma agrees in possessing the characteristic features of the legion, and thus justifies its derivation monophyletically from the common stem-form Actissa, the different forms of skeleton, on the other hand, cannot all be referred to the same fundamental form. More especially the spherical lattice-shell, from which all the numerous skeletal forms of the SphÆrellaria may be derived, cannot have arisen from the incomplete Beloid skeleton which characterises the Beloidea among the Collodaria. It is probable rather that the formation of the skeleton has taken place independently in those two groups of Spumellaria. From the skeletonless Colloidea, as the common stem-group of the Spumellaria, two different main groups have diverged, on the one hand the Beloidea, whose skeleton consists of separate spicules scattered in the extracapsulum, and on the other hand, the SphÆrellaria, which have formed a simple lattice-sphere around the central capsule; from this the manifold forms of the remaining Spumellaria may be derived.

If in the SphÆroidea the characteristic number and disposition of the radial spines be regarded as the most important heritable peculiarity of the different families, then we have the following natural arrangement:—(1) LiosphÆrida, without radial spines; (2) CubosphÆrida, with six radial spines (opposite in pairs in three axes perpendicular to each other); (3) StaurosphÆrida, with four radial spines (in two axes crossed at right angles); (4) StylosphÆrida, with two opposite radial spines (in the vertical main axis); and (5) AstrosphÆrida, with numerous regularly or irregularly distributed radial spines (eight to twenty or more). If, on the contrary, more stress be laid upon the number of the concentric lattice-shells, then we have the following artificial grouping:—(1) MonosphÆrida, with one simple lattice-sphere; (2) DyosphÆrida, with two concentric lattice-spheres; (3) TriosphÆrida, with three; (4) TetrasphÆrida, with four; (5) PolysphÆrida, with numerous (five to twenty or more) concentric lattice-shells; (6) SpongosphÆrida, with a spongy spherical shell. In general the former arrangement appears more natural than the latter, since the number of primary radial spines, which grow out from the primary lattice-sphere, determines their ground-form from the outset, whatever may be the number of secondarily added shells. Strictly speaking, according to the view adopted, these LiosphÆrida which have several shells, on the outer surface of which there are no radial spines, ought to be classified according to the number and arrangement of their internal radial connecting beams and distributed among the other families. The practical application of this correct principle meets, however, with great difficulties. Also in many cases the phylogenetic relations of the different SphÆroidea are more complicated than would appear from both these classificatory principles. In general their phylogeny will quite correspond with their ontogeny, since from the innermost first formed lattice-shell (primary medullary shell) a number of radial spines arises, and upon these the secondary shells are formed from within outwards.

169. Phylogeny of the Acantharia.—The legion Acantharia or Actipylea is distinguished by its peculiar acanthin skeleton, which develops centrogenously, as well as by the disposition in groups of the pores in its central capsule, and its excentric usually precocious nucleus; it is thus so different from all other Radiolaria as undoubtedly to furnish, phylogenetically considered, an independent stem (§ 7). This stem is only connected at the root by Actinelius with the primitive form of the Spumellaria, Actissa. The stem is monophyletic, since all the forms belonging to it may be derived without violence from Actinelius as a common primitive form.

171. Hypothetical Genealogical Tree of the Acantharia:—

Diploconida
 
Phractopeltida Hexalaspida Cenocapsida
Phatnaspida Lychnaspida
Porocapsida
Coleaspida  
Ceriaspida  
 
Belonaspida  
Phractaspida Stauraspida
Astrocapsida
SphÆrocapsida
 
 
Diporaspida
(Dorataspida dipora)		 Tessaraspida
(Dorataspida tetrapora)
 
 
[Dorataspida]
 
 
Quadrilonchida
Phractacanthida Stauracanthida
Amphilonchida
 
Acanthonia
 
 
Astrolonchida
Litholophida Chiastolida
Zyganthida
Acanthonida Actinastrum
Acanthometron
Astrolophida Acanthochiasmida
 
Acanthometron
 
 
Actinelida
Actinelius
 
Actissa
                                                                                                                                                         
Diploconida
 
Phractopeltida Hexalaspida Cenocapsida
 
Phatnaspida Lychnaspida
 
Porocapsida
Coleaspida  
Ceriaspida  
 
Belonaspida  
Phractaspida Stauraspida
Astrocapsida
SphÆrocapsida
 
 
Diporaspida
(Dorataspida dipora)		 Tessaraspida
(Dorataspida tetrapora)
 
 
[Dorataspida]
 
 
Quadrilonchida
 
Phractacanthida Stauracanthida
Amphilonchida
 
Acanthonia
 
 
Astrolonchida
 
Litholophida Chiastolida
 
Zyganthida
Acanthonida Actinastrum
Acanthometron
Astrolophida Acanthochiasmida
 
Acanthometron
 
 
Actinelida
Actinelius
 
Actissa

172. Adelacantha and Icosacantha.—The numerous forms of Acantharia, here disposed in twelve families and sixty-five genera, may be divided phylogenetically into two main groups of very different extent—Adelacantha and Icosacantha. The more primitive group, Adelacantha, have an indefinite and variable number of radial spines, which are always quite simple in form and usually irregularly distributed; this main division includes only the one order Actinelida, with six genera, among which is Actinelius, the common stem-form of all the Acantharia. The more recent group, Icosacantha, includes all the other Acantharia (fifty-nine genera), and is very markedly distinguished from the Adelacantha by the fact that the radial spines are always twenty in number, and arranged according to MÜller's law (compare pp. 717-725, and § 110). Since this regular disposition (in five alternating zones each of four spines) has been retained by inheritance in the whole of the Icosacantha, it is probable that this large group has been developed monophyletically from a twig of the Adelacantha; Actinastrum (p. 732) and Chiastolus (p. 738) still present connecting links between the former and the latter, between Actinelius and Acanthometron.

180. Hypothetical Genealogical Tree of the Nassellaria.

Cyrtoidea
brace
Botryodea
brace		 Triradiata
Pylobotryida Podocampida
Eradiata Multiradiata Spyroidea
brace
Lithocampida Phormocampida Androspyrida
Lithobotryida Podocyrtida
Theocyrtida Phormocyrtida Tholospyrida
Cannobotryida Tripocyrtida Phormospyrida
Sethocyrtida Anthocyrtida
Tripocalpida
Cyrtocalpida PhÆnocalpida
Stephoidea
brace		  
Tympanida Zygospyrida
(Spyroidea triradiata)
Tripocalpida
(Cyrtioidea triradiata monocyrtida)
Coronida
Semantida
 
Cyrtellaria
Cortiniscus
Stephanida  
 
 
Cortina * long dash Cortinida (Plectellaria)
(Cortina)
 
Plectaniscus long dash Plagoniscus long dash brace
  Plectoidea
Tetraplecta long dash Tetraplagia long dash Plectanida
 
Plectophora long dash Plagiacantha long dash
  Plagonida
Triplecta long dash Triplagia long dash
 
Nassoidea
(Nassellida)
 
Nassella
(Cystidium)
 
Actissa
                                                                                                                                 
Cyrtoidea
brace
Botryodea
brace		 Triradiata
Pylobotryida Podocampida
Eradiata Multiradiata Spyroidea
brace
Lithocampida Phormocampida
 
Lithobotryida Podocyrtida Androspyrida
 
Theocyrtida Phormocyrtida Tholospyrida
 
Cannobotryida Tripocyrtida Phormospyrida
 
Sethocyrtida Anthocyrtida
 
Tripocalpida
 
Cyrtocalpida PhÆnocalpida
 
Zygospyrida
(Spyroidea triradiata)
Tripocalpida
(Cyrtioidea triradiata monocyrtida)
 
 
Stephoidea
brace
Tympanida
  Cyrtellaria
Coronida
Semantida
 
Cortiniscus
Stephanida  
   
   
Cortina * —— Cortinida (Plectellaria)
(Cortina)
 
Plectaniscus —— Plagoniscus brace
  Plectoidea
Tetraplecta —— Tetraplagia Plectanida
 
Plectophora —— Plagiacantha
  Plagonida
Triplecta —— Triplagia
 
Nassoidea
(Nassellida)
 
Nassella
(Cystidium)
 
Actissa

192. Phylogeny of the PhÆodaria.—The legion PhÆodaria or Cannopylea is so clearly marked off from other Radiolaria by the double membrane of the central capsule and the astropyle at its oral pole, as well as by the extracapsular phÆodium, that it must be regarded phylogenetically as an independent stem (§ 9). This stem is only connected at its root by PhÆodina with the stem-form of the Spumellaria, Actissa. The stem itself is monophyletic, inasmuch it its members may be derived without violence from the skeletonless PhÆodinida (PhÆodina, PhÆocolla). On the other hand, the formation of the skeleton of the PhÆodaria is undoubtedly polyphyletic, different PhÆodinida having independently commenced the formation of a skeleton and having carried it out in very different ways.

194. Hypothetical Genealogical tree of the PhÆodaria:—

PhÆoconchia
brace
PhÆosphÆria Coeloplegmida PhÆogromia
brace brace
Aularida Tuscarorida
Coelodrymida
Aulonida
Coelotholida
Coelographida		 Haeckelinida
 
Conchopsida Coelodorida
AulosphÆrida Coelodendrida Circogonida
 
Conchasmida
Concharida
Sagmarida
 
Castanellida Circoporida
CannosphÆrida
Oroscenida Concharida
Sagenida
SagophÆrida		 Gazellettida
Oronida
OrosphÆrida		 Pharyngellida
 
Euphysettida
Medusettida		  
 
Lithogromida
Challengerida
PhÆodinida  
 
 
PhÆocystina
brace
Aulacanthida
 
Cannobelida Catinulida
 
Dictyochida  
 
PhÆodinida
Cannorrhaphida PhÆodinida
 
 
PhÆodina
 
(PhÆometra)
 
Actissa
                                                                                                                             
PhÆoconchia
brace
PhÆosphÆria Coeloplegmida
brace
Aularida
Coelodrymida
Aulonida
Coelotholida
Coelographida
 
Conchopsida Coelodorida
AulosphÆrida Coelodendrida
 
Conchasmida
Concharida
Sagmarida
 
 
CannosphÆrida
Oroscenida Concharida
Sagenida
SagophÆrida
Oronida
OrosphÆrida
 
 
 
PhÆodinida
 
≈
 
 
PhÆogromia
brace
Tuscarorida
Haeckelinida
 
Circogonida
 
 
Castanellida Circoporida
 
Gazellettida
Pharyngellida
 
Euphysettida
Medusettida		  
 
Lithogromida
Challengerida
 
 
PhÆocystina
brace
Aulacanthida
 
Cannobelida Catinulida
 
Dictyochida  
 
 
PhÆodinida ≈ PhÆodinida
 
Cannorrhaphida PhÆodinida
 
 
PhÆodina
 
(PhÆometra)
 
Actissa

195. PhÆocystina and PhÆocoscina.—Whilst the malacoma of all PhÆodaria possesses the characteristics of the legion, and hence justifies the assumption of a monophyletic origin, the skeleton, on the other hand, shows in the different groups such manifold and fundamental variations that a polyphyletic origin of the latter is indubitable. Different PhÆodinida have commenced the formation of the skeleton independently, and it has progressed in different directions. In the PhÆocystina it remained incomplete and led to the formation of various Beloid skeletons, whilst the PhÆocoscina developed complete lattice-shells. Both of these divisions too are to be regarded as polyphyletic, since the skeletal forms of the different groups cannot be derived without violence from a common primitive form.

200. The Fundamental Biogenetic Law.—The causal connection between ontogeny and phylogeny, which finds its most precise statement in the fundamental biogenetic law, holds in general for the Radiolaria as for all other organisms. In order to furnish direct proof of this, however, a complete empirical knowledge both of individual and of palÆontological development would be necessary. In both these directions, as has been shown in the foregoing chapters, our knowledge of the Radiolaria is very incomplete and fragmentary, but still we are able to convince ourselves indirectly of the validity of the law as applied to Radiolaria by the aid of comparative anatomy. This is now so fully known to us (§§ 1-140) that we are able not only to draw a complete and satisfactory picture of their morphology, but also to arrive at most important conclusions regarding the ontogeny and phylogeny of the individual groups. As regards the formation of the multiform skeleton of the Radiolaria, most of the ontogenetic series of forms, with which we have become acquainted by comparative anatomy, are of palingenetic nature; that is, they are primarily due to inheritance and thus of direct phylogenetic significance. On the other hand, among the ontogenetic phenomena of the Radiolaria, as far as they have yet been investigated, only very few are cenogenetic, that is, brought about by adaptive modification and without direct significance as regards phylogeny.

PHYSIOLOGICAL SECTION.

Chapter VII.—VEGETATIVE FUNCTIONS.

(§§ 201-217.)

201. Mechanism of the Functions.—The vital phenomena of the Radiolaria are dependent upon the mechanical functions of their unicellular body, and like those of all other organisms, are to be referred to physical and chemical natural laws. All processes which appear in the life of the Radiolaria are, therefore, ultimately to be explained by the attraction and repulsion of the smallest particles, which compose the different portions of their unicellular body; and the sensation of pleasure or the opposite is in its turn the exciting cause of these elementary movements. Many adaptive arrangements in the Radiolarian organism may produce the appearance of being the premeditated result of causes working towards an end ("zweckthÄtig," causÆ finales), but as opposed to this deceptive appearance it must here be expressly stated that these may be recognised in accordance with the developmental theory as the necessary consequence of mechanical causes (causÆ efficientes).

Our physiological acquaintance with the Radiolaria has by no means progressed so far as our morphological, so that the incomplete communications which are placed here for the sake of completeness must be regarded merely as preliminary fragments, not as fully elaborated results. Since my recent investigations have been mainly in the direction of morphology, I can add but little to the physiological conclusions, which I stated at length in my monograph twenty-four years ago (L. N. 16, pp. 127-165). Recently the vegetative physiology of the Radiolaria has been much advanced by the recognition of the symbiosis with the XanthellÆ (§ 205, L. N. 22, 39, 42). In addition Karl Brandt has recently (1885) published several important contributions to the physiology of the Polycyttaria or Sphaerozoea (L. N. 52).

202. Distribution of Functions.—The distribution of the functions among the various parts of the unicellular organism of the Radiolaria corresponds directly to their anatomical composition, so that physiologically as well as morphologically the central capsule and the extracapsulum appear as the two coordinated main components. On the one hand the central capsule with its endoplasm and enclosed nucleus is the central organ of the "cell-soul" (Zellseele), the unit regulating its animal and vegetative functions, and the special organ of reproduction and inheritance. The extracapsulum forms, on the other hand, by its calymma the protective envelope of the central capsule, the support of the soft pseudopodia and the substratum of the skeleton; the calymma acts also as a hydrostatic apparatus, whilst the radiating pseudopodia are of the greatest importance both as organs of nutrition and adaptation, as well as of motion and sensation (§ 15). If, however, the vital functions as a whole be divided in accordance with the usual convention into the two great groups of vegetative (nutrition and reproduction) and animal (motion and sensation), then the central capsule would be mainly the organ of reproduction and sensation, and the extracapsulum the organ of nutrition and motion.

The numerous separate vital phenomena, which by accurate physiological investigation may be distinguished in the unicellular Radiolarian organism, may be distributed in the above indicated conventional fashion into a few larger and several smaller groups; it must always be borne in mind, however, that these overlap in many respects, and that the division of labour among the different organs in these Protista is somewhat complicated, notwithstanding the apparent simplicity of their unicellular organization. A general classification of the groups of functions is difficult, because each individual organ discharges several different functions. Thus the central capsule is pre-eminently the organ of reproduction and inheritance, but not less (though less conspicuous) is its importance as the psychical central organ, the unit regulating the processes of sensation, motion, and also nutrition. In this last respect it is comparable to the nerve-centres of the Metazoa, whilst the peripheral nervous system of the latter (including the organs of sense and the muscles) are in the present instance represented by the pseudopodia, which are at the same time the most important organs of nutrition and adaptation. In the calymma also in similar fashion several different physiological functions are united.

203. Metastasis.—The functions of metastasis and nutrition have in all Radiolaria a purely animal character, so that these Rhizopoda from the physiological standpoint are to be regarded as truly unicellular animals, or Protozoa ("Urthiere"). Since they do not possess, like plants, the power of forming synthetically the compounds (protoplasm, carbohydrates, &c.) necessary for their sustenance, they are compelled to obtain them ready-formed from other organisms. Like other true animals they evolve carbon dioxide by the partial oxidation of those products, and hence they successively take up the oxygen necessary to their existence from their environment.

The question whether the Radiolaria are to be regarded as true animals I discussed fully from various points of view in 1862, and finally answered in the affirmative (L. N. 16, pp. 159-165). Afterwards, when in my Generelle Morphologie (1866) I sought to establish the kingdom Protista, I removed the Radiolaria along with the other Rhizopoda from the animal kingdom proper and placed them in the kingdom Protista (Bd. i. pp. 215-220; Bd. ii. p. xxix). Compare also my Protistenreich (L. N. 32) and my NatÜrliche SchÖpfungsgeschichte (vii. Aufl., 1879, p. 364). Both these steps appear fully justified when considered in the light of our present increased knowledge. From the physiological standpoint the Radiolaria appear as unicellular animals, for in this respect the animal character of their metastasis (that proper to an oxidising organism) furnishes the sole criterion. On the other hand, from the morphological standpoint, they are to be classed as neutral Protista, for in this respect their unicellular character is the prominent feature, and distinguishes them from all true multicellular animals (Metazoa). Compare my GastrÆa Theorie (1873, Jena. Zeitschr. fÜr Naturwiss., Bd. viii. pp. 29, 53).

204. Nutrition.—The nutritive materials which the Radiolaria require for their sustenance, especially albuminates (plasma) and carbohydrates (starch, &c.), they obtain partly from foreign organisms which they capture and digest, and partly directly from the XanthellÆ or Philozoa, the unicellular AlgÆ, with which they live in symbiosis (§ 205). Zooxanthella intracapsularis, found in the Acantharia (§ 76), is probably of the same significance in this respect as Zooxanthella extracapsularis of the Spumellaria and Nassellaria (§ 90); and perhaps the same is true also of PhÆodella extracapsularis (or Zoochlorella phÆodaris?) of the PhÆodaria (§ 89). The considerable quantity of starch or amyloid bodies, elaborated by these inquiline symbiontes, as well as their protoplasm and nucleus, are available, on their death, for the nutrition of the Radiolaria which harbour them. Nutrition by means of other particles obtained by the pseudopodia from the surrounding medium is by no means excluded; indeed it may be regarded as certain that numerous Radiolaria (especially such as contain no symbiotic Algoid cells) are nourished for the most part or exclusively by this means. Diatoms, Infusoria, Thalamophora (Foraminifera) as well as decaying particles of animal and vegetable tissues can be seized directly by the pseudopodia and conveyed either to the sarcodictyum (on the surface of the calymma) or to the sarcomatrix (on the surface of the central capsule) in order to undergo digestion there. The indigestible constituents (siliceous shells of Diatoms and Tintinnoidea, calcareous shells of small Monothalamia and Polythalamia, &c.) are here collected often in large numbers and removed by the streaming of the protoplasm.

The inception and digestion of nutriment, as it usually appears to take place by the pseudopodia, has already been so fully treated in my Monograph (L. N. 16, pp. 135-140), and since then in my paper on the sarcode body of the Rhizopoda (L. N. 19, p. 342), that I have nothing of importance to add. Quite recently Karl Brandt has expressed a doubt as to whether the taking up of formed particles by the pseudopodia and their aggregation in the calymma be really connected with the process of nutrition. He is disposed rather to believe that these foreign bodies are usually only accidentally and mechanically brought into the calymma, and that the nourishment of the Radiolaria is derived exclusively or pre-eminently from the symbiotic XanthellÆ (L. N. 52, pp. 88-93). I must, however, maintain my former opinion, which I have only modified insomuch that I now regard the sarcodictyum (on the outer surface of the calymma, § 94) rather than the sarcomatrix (on the outer surface of the central capsule, § 92) as the principal seat of true digestion and assimilation. From the sarcodictyum the dissolved and assimilated nutritive matters may pass by the intracalymmar pseudopodia (or sarcoplegma, § 93) into the sarcomatrix, and hence may reach the endoplasm through the openings in the central capsule. To what an extent the Radiolaria are capable of taking up even large formed bodies into the calymma, is shown by the striking instance of Thalassicolla sanguinolenta, which becomes so deformed by the inception of numerous coccospheres and coccoliths, that I described it as a special genus under the name Myxobrachia (compare pp. 23, 30; also L. N. 21, p. 519, Taf. xviii., and L. N. 33, p. 37).

205. Symbiosis.—Very many Radiolaria, but by no means all members of this class, live in a definite commensal relation with yellow unicellular AlgÆ of the group XanthellÆ. In the Acantharia they live within the central capsule (Zooxanthella intracapsularis, § 76), in the Spumellaria and Nassellaria, on the other hand, within the calymma but outside the central capsule (Zooxanthella extracapsularis, § 90); in the PhÆodaria a special form of these symbiotic unicellular AlgÆ appears to inhabit the phÆodium in the extracapsulum, and to compose a considerable portion of the phÆodellÆ (Zooxanthella phÆodaris, § 90, or better perhaps Zoochlorella phÆodaris, § 89). Undoubtedly this commensal life is in very many cases of the greatest physiological significance for both the symbiontes, for the animal Radiolarian cells furnish the inquiline XanthellÆ not only with shelter and protection, but also with carbon dioxide and other products of decomposition for their nutriment; whilst on the other hand the vegetable cells of the XanthellÆ yield the Radiolarian host its most important supply of nutriment, protoplasm and starch, as well as oxygen for respiration. Hence it is not only theoretically possible, but has been experimentally proved, that Radiolaria which contain numerous XanthellÆ can exist without extraneous nutriment for a long period in closed vessels of filtered sea-water, kept exposed to the sunlight; the two symbiontes furnish each other mutually with nourishment, and are physiologically supplementary to each other by reason of the opposite nature of their metastasis. This symbiosis is not necessary, however, for the existence of the Radiolaria; for in many species the number of XanthellÆ is very variable and in many others they are entirely wanting.

The symbiosis of the Radiolaria and XanthellÆ, or "yellow cells" (§§ 76, 90) was first discovered by Cienkowski in 1871 (L. N. 22). Ten years later this important and often doubted fact was established by extended observations and experiments almost simultaneously by Karl Brandt (L. N. 38, 39) and Patrick Geddes (L. N. 42, 43). This commensal life may be compared with that of the lichens, in which an organism with vegetable metastasis (the Algoid gonidia) and an organism with animal metastasis (the Fungoid hyphÆ) are intimately united for mutual benefit. But the symbiosis of the XanthellÆ and Radiolaria is not as in the lichens a phenomenon essential for their development, but has more or less the character of an accidental association. The number of the inquiline XanthellÆ is so variable even in one and the same species of Radiolaria, that they do not appear to be exactly essential to its welfare; and in many species they are entirely wanting. Their significance is questionable in the case of those numerous deep-sea Radiolaria which live in complete darkness, and in which, therefore, the XanthellÆ, even if present, could excrete no oxygen on account of the want of light. Nevertheless it is possible that the phÆodellÆ of the PhÆodaria (usually green, olive, or brown in colour), which are true cells, represent vegetable symbiontes, which in the absence of sunlight are able to evolve oxygen by the aid of the phosphoresence of other abyssal animals. Since the PhÆodaria are, for the most part, dwellers in the deep-sea, and since the voluminous phÆodium must be of great physiological importance, a positive solution of this hypothetical question would be of no small interest (compare § 89).

206. Respiration.—The respiration of the Radiolaria is animal in nature, since all Protista of this class, like all other true Rhizopoda, take in oxygen and give off carbon dioxide. Probably this process goes on continuously and is tolerably active, as may be inferred from the fact that Radiolaria cannot be kept for long in small vessels of sea-water unless either they contain numerous XanthellÆ or the water is well aËrated. The oxygen is obtained from two sources, either from the surrounding water or from the enclosed XanthellÆ, which in sunlight evolve considerable quantities of this gas. Correspondingly, the carbon dioxide which is formed during the process of oxidation of the Radiolaria is either given up to the surrounding water or to the inquiline XanthellÆ, which utilise it for their own sustenance (§§ 204, 205).

The significance of the symbiotic XanthellÆ for the respiration of the enclosing Radiolaria may be shown experimentally in the following way. If two Polycyttarian colonies of equal size, both of which contain numerous XanthellÆ, be placed in equal quantities of filtered sea-water in sealed glass tubes, and if one tube be placed in the dark the other in the light, the colony in the former rapidly perishes, but not that in the latter; the XanthellÆ excrete only under the influence of sunlight the oxygen necessary for the life of the Radiolarian (compare Patrick Geddes, L. N. 42, p. 304).

207. Circulation.—In the protoplasm of all Radiolaria, both inside and outside the central capsule, slow currents may be recognised which fall under the general term circulation, and have already been compared to the cyclosis in the interior of animal and vegetable cells, as well as to the sarcode streams in the body of other Rhizopoda. These plasmatic currents or "plasmorrheumata" probably continue throughout the whole life of the Radiolaria, and are of fundamental importance for the performance of their vital functions. They depend upon slow displacements of the molecules of the plasma (plastidules or micellÆ) and cause a uniform distribution of the absorbed nutriment and a certain equalisation of the metastasis. Furthermore they are of great importance also in the inception of nutriment, the formation of the skeleton, locomotion, &c. Sometimes the circulation is directly perceptible in the plasma itself; but usually it is only visible owing to the presence of granules (sarcogranula), which are suspended in the plasma in larger or smaller numbers. The movements of these granules are usually regarded as passive, due to the active displacement of the molecules of the plasma. Although the intracapsular protoplasm is in communication with the extracapsular through the openings in the capsule membrane, nevertheless the currents exhibit certain differences in the two portions of the malacoma. It is sometimes possible, however, to recognise the direct connection between them and to observe how the granules pass through the openings in the capsule-membrane.

208. Currents in the Endoplasm.—Intracapsular circulation or a certain slow flowing of the plasma within the central capsule is probably just as common in the Radiolaria as without it, but it is not so easy to observe in the former case as in the latter. A more satisfactory proof of these endoplasmatic currents is furnished by the arrangement of the protoplasm within the central capsule, since this is (at all events in part) an effect produced by them. In this respect the two main divisions of the class show characteristic differences. In the Porulosa (the Spumellaria, § 77, and the Acantharia, § 78) the endoplasm is in general distinguished by a more or less distinct radial structure, which is to be regarded as the effect of alternating centripetal and centrifugal radial streams. In the Osculosa, on the other hand, this radial structure is absent and the intracapsular plasmatic streams converge or diverge towards the osculum or main-opening in the central capsule which lies at the basal pole of its main axis, and through which the mass of the endoplasm issues into the calymma. The two legions of the Osculosa, however, present differences in this respect. In the Nassellaria (§ 79) the endoplasmatic currents appear to unite in an axial main stream at the apex of the monaxon central capsule, and this apical stream seems to split into a conical bundle, the individual threads of which pass diverging between the myophane fibrillÆ of the podoconus towards the basis of the central capsule, and issue through the pores of the porochora. In the PhÆodaria (§ 80), on the other hand, meridional currents of endoplasm are probably present on the inner surface of the capsule, which flow from the aboral pole of the vertical main axis to its basal pole, and return in the reverse direction.

209. Currents in the Exoplasm.—Extracapsular circulation, or a distinct flowing of the plasma outside the central capsule, may be readily observed in all Radiolaria which are examined alive; this is most readily seen in the astropodia, or those free pseudopodia which radiate from the sarcodictyum on the surface of the calymma into the surrounding water. The granular movement is often quite as clear in the sarcodictyum itself, and may be recognised in the collopodia, which compose the irregular plasmatic network within the calymma. More rarely it is possible to follow the granular stream thence through the sarcomatrix, and further into the interior of the central capsule. In general the direction of the extracapsular protoplasmic streams is radial, and it is frequently possible, even in a single free astropodium, to observe two streams opposite in direction, the granules on one side of the radial sarcode thread moving centripetally, those on the other side centrifugally. If the threads branch, and neighbouring ones become united by connecting threads, the circulation of the granules may proceed quite irregularly in the network thus formed. The rapidity and character of the extracapsular currents are subject to great variations.

The different forms of extracapsular sarcode currents have been already very fully described in my Monograph (L. N. 16, pp. 89-126), and in my critical essay on the sarcode body of the Rhizopoda (L. N. 19, p. 357, Taf. XXVI.).

210. Secretion.—Under the name secretions, in the strict sense, all the skeletal formations of the Radiolaria may be included. They may be divided according to their chemical composition into three different groups: pure silica in the Spumellaria and Nassellaria, a silicate of carbon in the PhÆodaria, and acanthin in the Acantharia (compare § 102). It may indeed be assumed that these skeletons arise directly by a chemical metamorphosis (silicification, acanthinosis, &c.) of the pseudopodia and protoplasmic network; and this view seems especially justified in the case of the Astroid skeleton of the Acantharia (§ 114), the Spongoid skeleton of the Spumellaria (§ 126), the Plectoid skeleton of the Nassellaria (§ 125), the Cannoid skeleton of the PhÆodaria (§ 127), and several other types. On closer investigation, however, it appears yet more probable that the skeleton does not arise by direct chemical metamorphosis of the protoplasm, but by secretion from it; for when the dissolved skeletal material (silica, acanthin) passes from the fluid into the solid state, it does not appear as imbedded in the plasma, but as deposited from it. However, it must be borne in mind that a hard line of demarcation can scarcely, if at all, be drawn between these two processes. In the Acantharia the intracapsular sarcode is the original organ of secretion of the skeleton; in the other three legions, on the other hand, the extracapsulum performs this function (§§ 106, 107). In addition to the skeleton, we may regard as secretions (or excretions) the intracapsular crystals (§ 75) and concretions (§ 75A), and perhaps certain pigment-bodies (§§ 74, 88); and further, the calymma (§ 82) may be considered to be a gelatinous secretion of the central capsule, and perhaps also the capsule-membrane, in so far as it represents only a secondary excretory product of the unicellular organism.

211. Adaptation.—The innumerable and very various adaptive phenomena which we meet with in the morphology of the Radiolaria, and especially in that of their skeleton, are like other phenomena of the same kind, to be ultimately referred to altered nutritional relations. These may be caused directly either by the influence of external conditions of existence (nutrition, light, temperature, &c.), or by the proper activity of the unicellular organism (use or disuse of its organs, &c.), or, finally, by the combined action of both causes in the struggle for existence. In very many cases the cause to which the origin of a particular form of Radiolaria is due may be directly perceived or at least guessed at with considerable probability; thus, for example, the lattice-shells may be explained as protective coverings, the radial spines as defensive weapons, and the anchor-hooks and spathillÆ as organs of prehension, which are of advantage to their possessors in the struggle for existence; the regular arrangement of the radial spines in the Radiolaria may also be explained on hydrostatic grounds, it being advantageous that the body should be maintained in a definite position of equilibrium, &c. The well-known laws of direct or actual adaptation, which we designate cumulative, correlative, divergent adaptation, &c., here explain a multitude of morphological phenomena. The connection is less distinct in the case of the laws of indirect or potential adaptation, although this must play as important a part in the formation of the Radiolaria as in that of other organisms (compare on this head my Generelle Morphologie, Bd. ii. pp. 202-222).

212. Reproduction.—The most common form of reproduction in the Radiolaria is the formation of spores in the central capsule, which in this respect is to be regarded as a sporangium (§ 215). In many Radiolaria (Polycyttaria and PhÆodaria), however, there occurs in addition an increase of the unicellular organism by simple division (§ 213); upon this the formation of colonies in the social Radiolaria is dependent (§ 14). Reproduction by gemmation is much less common, and has hitherto been observed only in the Polycyttaria (§ 214). In this group alone there also occur at certain times two different forms of swarm-spores which copulate, and thus indicate the commencement of sexual reproduction (Alternation of Generations, § 216). The general organ of reproduction is in all cases the central capsule, whilst the extracapsulum never takes an active part in the process.

214. Cell-Gemmation.—Reproduction by gemmation has hitherto been observed only in the social Radiolaria, but in them it appears to be widely distributed, and in very young colonies is perhaps almost universally present. The gemmules or capsular buds (hitherto described as "extracapsular bodies") are developed on the surface of young central capsules before these had secreted a membrane. They grow usually in considerable numbers, from the surface of the central capsule, which is sometimes quite covered with them. Each bud usually contains a raspberry-like bunch of shining fatty globules, and by means of reagents a few larger or a considerable number of smaller nuclei may be recognised in them; the naked protoplasmic body of the bud is not enclosed by any membrane. As soon as the buds have reached a certain size they are constricted off from the central capsule and separated from it, being distributed in the meshes of the sarcoplegma by the currents in the exoplasm. Afterwards each bud becomes developed into a complete central capsule by surrounding itself with a membrane when it has attained a definite size. From the special relations of the process of nuclear formation, which take place in the multiplication of the social central capsules by gemmation and by cell-division, it would appear that the capsules produced by the former method afterwards produce anisospores, whilst those in the latter way yield isospores (§ 216).

The gemmules or capsular buds of the Polycyttaria were first accurately described by Richard Hertwig (L. N. 26, pp. 37-39), under the name "extracapsular bodies," and their significance rightly indicated; earlier observers had incidentally mentioned and figured them, but had not seen their origin from the central capsule. Quite recently Karl Brandt has given a very painstaking account of them in the different Polycyttarian genera (L. N. 52, pp. 179-198). In the Monocyttaria such a formation of buds has not yet been observed. The basal lobes of the central capsule, which occur in many Nassellaria, are not buds, but simple processes of the capsule, due to its protrusion through the collar pores of the cortinar septum (§ 55).

215. Sporification.—Asexual reproduction by the formation of movable flagellate spores has been hitherto observed only in a very small number of genera; but since these belong to very different groups, and since the comparative morphology of the capsule appears to be similar throughout as regards the structure and development of its contents, it may be safely assumed that this kind of reproduction occurs quite generally in the Radiolaria. In all cases it is the contents of the central capsule, from which the swarm-spores are formed, both nucleus and endoplasm taking an equal share in the process; in all cases the spores produced are very numerous, small, ovoid or reniform, and have one or two very long slender flagella at one extremity (see §§ 141, 142). Since the whole contents of the mature central capsule are used up in the formation of these flagellate zoospores, it discharges the function of a sporangium. The division of the simple primary nucleus into numerous small nuclei, which usually (serotinous Radiolaria) takes place only shortly before sporification, but sometimes (precocious Radiolaria, § 63) happens very early, is the commencement of the often repeated process of nuclear division, which terminates with the production of a very large number of small spore-nuclei. The nucleolus often divides very peculiarly (§ 69, C). Each spore nucleus becomes surrounded by a portion of endoplasm and usually receives in addition one or more fatty granules, and sometimes also a small crystal (hence the "crystal-spores"). The size of the flagellate zoospores which emerge from the ruptured central capsule and swim freely in the water by means of their flagellum, varies generally between 0.004 and 0.008 mm. The extracapsulum is not directly concerned in the sporification, but undergoes degeneration during the process and perishes at its conclusion.

The first complete and detailed observations on the formation of spores in the Radiolaria were published by Cienkowski in 1871 and related to two genera of Polycyttaria, the skeletonless Collozoum and the spherical-shelled CollosphÆra (L. N. 22, p. 372, Taf. xxix.). These were subsequently continued and supplemented by R. Hertwig (1876, L. N. 26, pp. 26-42, and L. N. 33, p. 129), and a general summary of these results has been given by BÜtschli (L. N. 41, pp. 449-455). Recently Karl Brandt has given a very detailed and fully illustrated account of the sporification of the Polycyttaria (L. N. 52, pp. 145-178). I have also had the opportunity during my sojourn in the Canary Islands (1866), in the Mediterranean at Corfu (1877), and Portofino (1880), as well as in Ceylon (1881), of observing the development of flagellate zoospores from the central capsule of individuals of all four legions: among the Spumellaria in certain Colloidea, Beloidea, SphÆroidea, and Discoidea, among the Acantharia in several Acanthometra and Acanthophracta, among the Nassellaria in individuals belonging to the Stephoidea, Plectoidea, and Cyrtoidea, and among the PhÆodaria in one Castanellid. In most zoospores I could distinctly observe only a single long flagellum; sometimes, however, two or even three appeared to be present, but the determination of their number is very difficult.

216. Alternation of Generations.—A peculiar form of reproduction, which may be designated "alternation of generations," appears to occur generally in the Polycyttaria, but has not yet been observed in the Monocyttaria. All Collozoida, SphÆrozoida, and CollosphÆrida which have hitherto been carefully and completely examined with respect to their development, are distinguished by the production of two different kinds of swarm-spores, isospores and anisospores. The Isospores (or monogonous spores) correspond to the ordinary asexual zoospores of the Monocyttaria (§ 215); they possess a homogeneous, doubly refracting nucleus of uniform constitution and develop asexually, without copulation. The Anisospores (or amphigonous spores), on the other hand, are sexually differentiated and possess a heterogeneous, singly refracting nucleus of twofold constitution; they may therefore be distinguished as female macrospores and male microspores. The Macrospores (or gynospores, comparable with the female macrogonidia of many Cryptogams) are larger, less numerous, and possess larger nuclei, which are less easily stained, and have a fine filiform trabecular network. On the other hand the Microspores (or androspores, comparable with the male microgonidia) are much smaller and more numerous, and are distinguished by their smaller nuclei, which have thicker tuberculÆ and become stained more intensely. The gynospores and androspores are developed in the Collozoida and SphÆrozoida in the same individual, but not in the CollosphÆrida. It is very probable that these two forms of anisospores copulate with each other after their exit from the central capsule and thus produce a new cell by the simplest mode of sexual reproduction. But, since the same Polycyttaria, which produce these anisospores, at other times give rise to ordinary or asexual isospores, it is further possible that these two forms of reproduction alternate with each other, and that the Polycyttaria thus pass through a true alternation of generations. This has not yet been observed in the Monocyttaria, and hence these latter seem to bear to the Polycyttaria a relation similar to that in which the sexless solitary Flagellata (Astasiea) stand to the sexual social Flagellata (Volvocinea). In the two analogous cases the sexual differentiation may be regarded as a consequence of the social life in the gelatinous colonies.

The sexual differentiation of the Polycyttaria was first discovered in 1875 by R. Hertwig, and accurately described in the case of Collozoum inerme as occurring in addition to the formation of the ordinary crystal-spores (L. N. 26, p. 36); compare also the general discussion of BÜtschli (L. N. 41, p. 52). Recently Karl Brandt has demonstrated the formation of both homogeneous isospores (crystal-spores) and heterogeneous anisospores (macro- and microspores) in seven different species of Polycyttaria, and has come to the conclusion that in all social Radiolaria there is a regular alternation between the former and latter generations. Compare his elaborate account of the colonial Radiolaria of the Gulf of Naples (L. N. 52, pp. 145-178).

217. Inheritance.—Inheritance is to be regarded as the most important accompaniment to the function of reproduction, and especially in the present case, because the comparative morphology of the Radiolaria furnishes abundant instances of the action of its different laws. The laws of conservative inheritance are illustrated by the comparative anatomy of the larger groups; thus, in the four legions the characteristic peculiarities of the central capsule are maintained unaltered in consequence of continuous inheritance, although great varieties appear in the skeleton in each legion. The individual parts of the skeleton furnish by their development on the one hand and their degeneration on the other, especially in the smaller groups, examples of progressive inheritance. Thus in the Spumellaria the constant formation of the primary lattice-shell (a central medullary shell) and its ontogenetic relation to the secondary one, which is developed concentrically round it, can only be explained phylogenetically by conservative inheritance, whilst on the other hand the characteristic differentiation of the axes in the various families of Spumellaria is to be explained by progressive inheritance. In the Acantharia the arrangement of the twenty radial spines (in accordance with MÜller's law, §§ 110, 172) was first acquired by a group of the most archaic Actinelida (Adelacantha) through hydrostatic adaptation, and has since been transmitted by inheritance to all the other families of the legion (Icosacantha). The morphology of the Nassellaria is not less interesting, because here several different heritable elements (the primary sagittal ring and the basal tripod) combine in the most manifold ways in the formation of the skeleton (compare §§ 123, 124, 182). The affinities of the genera in the different families yield an astonishing variety of interesting morphological phenomena, which can only be explained by progressive inheritance. The same is true also of the PhÆodaria. In this legion the primary inheritance is especially manifested in the constant and firm structure of the central capsule with its characteristic double wall and astropyle, whilst the formation of the skeleton in this legion proceeds in different directions by means of divergent adaptation. The morphology of the Radiolaria thus proves itself a rich source of materials for the physiological study of adaptation and inheritance.

Chapter VIII.—ANIMAL FUNCTIONS.

(§§ 218-225.)

218. Motion.—In addition to the internal movements which appear generally in the unicellular Radiolaria and have already been mentioned as plasmatic currents in treating of the circulation (§§ 207-209), two different groups of external motor phenomena are to be observed in this class: first, the contraction of individual parts, which brings about modifications of form (§ 220), and secondly, voluntary or reflex locomotion of the whole body (§ 220). These movements are partly due to changes in form of undifferentiated plasmatic threads or sarcode filaments, partly to the actual contraction of differentiated filaments which are comparable to muscle fibrillÆ, and must therefore be distinguished as myophanes. In addition to this, endosmose and exosmose probably play an important part in some of the locomotive phenomena, but nothing is yet certainly known regarding these osmotic processes. We are at present equally ignorant whether all the movements of the Radiolaria are simply reflex (direct consequences of irritation) or whether they are in part truly spontaneous.

219. Suspension.—From direct observation of living Radiolaria, as well as from deductive reasoning, based upon their morphology (and especially their promorphology, §§ 17-50), the conclusion appears justified that all Protista of this class in their normal condition float suspended in the sea-water, either at the surface or at a definite depth. A necessary condition of this hydrostatic suspension is that the specific gravity of the Radiolarian organism must be equal to, or but slightly greater than that of sea-water. The increase in specific gravity brought about by the production of the siliceous skeleton, is compensated by the lighter fatty globules, and partly perhaps by the calymma, especially when the latter contains vacuoles or alveoles. The fluid or jelly contained in the latter appears to be for the most part lighter than sea-water (containing no salt, or only a very small quantity?). But if the specific gravity of the whole body should be generally (or perhaps always) slightly greater than that of sea-water, then the organism would be prevented from sinking, partly by the increased friction, due to the radiating pseudopodia and the radial spines usually present, and partly perhaps by active (if only feeble) movements of the pseudopodia.

220. Locomotion.—Active locomotion of the whole body, which is very probably to be regarded as voluntary, occurs in the Radiolaria in three different modes; (1) the vibratile movement of the flagellate swarm-spores; (2) the swimming of the floating organisms; (3) the slow creeping of those which rest accidentally upon the bottom. The vibratile movement of the swarm-spores is the result of active sinuous oscillation of the single or multiple flagellum, and is not essentially different from that of ordinary flagellate Infusoria (see note A). Of the active swimming of mature Radiolaria, only that form is known which is vertical in direction and causes the sinking and rising in the sea-water. This is probably, for the most part (perhaps exclusively), due to increase or diminution in the specific gravity, which is perhaps brought about by the retraction or protrusion of the pseudopodia; slow, oscillating, sinuous motions of these organs have been directly observed to take place (though very slowly) in suspended living Radiolaria. The most important hydrostatic organ is probably the calymma, by the contraction of which the specific gravity is increased, while it is diminished by its expansion; the contraction is probably brought about by active contraction of the sarcodictyum, and is connected with exosmosis, while the expansion is probably due to the elasticity of the calymma and the inception of water by endosmosis. In the Acanthometra (§ 96) the peculiar myophriscs appear to be charged with the duty of distending the gelatinous envelope, and thus diminishing the specific gravity; the latter increases again when the myophriscs are relaxed, and the calymma contracts by virtue of its own elasticity (see note B). The slow creeping locomotion exhibited by Radiolaria on a glass slide under the microscope, does not differ from that of the Thalamophora (Monothalamia and Polythalamia), but can only occur normally when the animal accidentally comes into contact with a solid surface or sinks to the bottom of the sea. Whether this actually occurs periodically is not known (see note C). The slow or gliding locomotion exhibited by creeping Monozoa on a glass slide is due to muscle-like contractions of bundles of pseudopodia, just as in the case of the social central capsules of Polyzoa, which live together in the same coenobium and are able to move within their common calymma sometimes centrifugally to its surface, sometimes towards the centre where they aggregate into a roundish mass (see note D).

A. Regarding the movement of the flagella in mature swarm-spores compare L. N. 22, p. 375; L. N. 26, pp. 31, 35; L. N. 41, p. 452, and L. N. 52, p. 170.

B. On the active vertical swimming movements of mature Radiolaria, especially the cause of sinking and rising, see L. N. 16, p. 134; L. N. 41, p. 443, and L. N. 52, pp. 97-102.

C. On the active horizontal creeping movements of mature Radiolaria on a firm ground, compare L. N. 12, p. 10, and L. N. 16, pp. 132-134.

D. Regarding the motion of social central capsules within the same coenobium and the changes thus brought about in the structure of the calymma, see L. N. 16, pp. 119-127, and L. N. 52, pp. 75-82.

221. Contraction.—Motions, which are due to the contraction of individual portions and cause changes in volume or form, have been partly already spoken of under the head of locomotion (§ 220) and are partly connected with other functions. Examples may be seen in the contraction of the central capsule and of the calymma. A certain contraction of the central capsule is probably brought about by the myophanes, which arise by differentiation of the endoplasm and hence may assume different forms in the four legions. In the Spumellaria, where numerous radial fibrillÆ run from the central nucleus to the capsule membrane (§ 77), the endoplasm is probably driven out evenly through all the pores of the capsule membrane by their simultaneous contraction, and hence the volume of the capsule is diminished in all directions. The Acantharia probably behave similarly, but are different, inasmuch as the number of their contractile radial fibrillÆ is less, and special axial threads (§ 78) are already differentiated. In the Nassellaria it is probable that owing to the contraction of the divergent myophane fibrillÆ in the podoconus the vertical axis of the latter is shortened, the opercular rods of the porochora are lifted, and the endoplasm driven out of its pores, so that the volume of the monaxon central capsule is diminished (§ 79). In the PhÆodaria the same result is probably brought about by the contraction of the cortical myophane fibrillÆ, which run meridionally along the inside of the capsule membrane from the apical to the basal pole of the vertical main axis, where they are inserted into the periphery of the astropyle; since the volume of the capsule is diminished by their contraction (their spheroidal figure becoming more nearly spherical) the endoplasm will be driven out through the proboscis of the astropyle. Whilst these contractions of the central capsule are largely due to differentiated muscle-like threads of endoplasm (myophanes), this appears to be but rarely the case with the contractions of the extracapsulum (e.g., the myophriscs of the Acanthometra, § 96). Most of the phenomena of contraction which can be observed in the calymma and pseudopodia depend upon exoplasmatic currents (§ 209).

222. Protection.—Of the utmost importance, both for the physiology and for the morphology of the Radiolaria are their manifold protective functions, which we now consider under the heading "protection." From the physiological point of view the consideration of the exposed situation in which the delicate, free-swimming Radiolarian organism lives, and the numerous dangers which beset it in the struggle for existence, would lead a priori to the expectation, that many special protective adaptations would be developed by natural selection. On the other hand, morphological experience shows us that this latter has been in action for immeasurable periods, and has gradually produced an abundance of the most remarkable protective modifications. Examples of these may be found in the formation of the voluminous calymma, as a gelatinous protective covering for the central capsule, and further, the formation of the capsule membrane itself, which separates the generative contents of the central capsule from the nutritive exoplasm. The phosphorescence of the central capsule, too (§ 223), may be regarded as a useful protective arrangement; as also the radiating of the numerous pseudopodia in all directions from the surface of the calymma; for they are of great significance to the well-being of the organism, both as sensory organs and as prehensile organs. By far the most important and most varied means for the actual defence of the soft body is to be seen in the endless modifications of the skeleton; first, in the production of the enclosing lattice-shells and projecting radial spines, but especially also in the very varied structure of the individual parts of the skeleton, and in the special differentiation of the small appendicular organs which grow out from it (hairs, thorns, spines, scales, spathillÆ, anchors, &c.). Finally "mimicry" possesses a considerable significance among the different forms of adaptation which are to be observed in this class.

223. Phosphorescence.—Many Radiolarians shine in the dark, and their phosphorescence presents the same phenomena as that of other luminous marine organisms; it is increased by mechanical and chemical irritation, or renewed if already extinguished. The light is sometimes greenish, sometimes yellowish, and appears generally (if not always) to radiate from the intracapsular fatty spheres (§ 73). Thus these latter unite several functions, inasmuch as they serve, firstly, as reserve stores of nutriment, secondly, as hydrostatic apparatus, and thirdly, as luminous organs for the protection of the Radiolaria; probably the light acts by frightening other animals, for the phosphorescent animals are provided with spines, nettle-cells, poison glands or other defensive weapons. The production of the light depends probably, as in other phosphorescent organisms, upon the slow oxidation of the fat-globules, which combine with active oxygen in the presence of alkalis. Phosphorescence is very likely widely distributed among the Radiolaria.

224. Sensation.—The general irritability which we ascribe to all organisms, and as the basis of which we regard the protoplasm, remains at an inferior stage of development in the Radiolaria. For although they are subject to various stimuli, and certainly possess a power of discrimination, special sensory organs are not differentiated; the peripheral portions of the protoplasm, and especially the pseudopodia, rather act both as organs of the different kinds of sensation and various modes of motion. That different Radiolaria have attained different degrees of development in this respect may be seen partly by direct observation of the reaction of the living organism towards various stimuli, and partly by the comparison of the different conditions of existence under which Radiolarians exist, both in the most various depths of the ocean and in all climatic zones (see note A). In general the Radiolaria seem to be sensitive to the following stimuli; (1) pressure (see note B); (2) temperature (see note C); (3) light (see note D); (4) chemical composition of the sea-water (see note E). The reaction towards these stimuli, corresponding to the sensation of pleasure or dislike which they call forth, is shown in various forms of motion of the protoplasm, changes in the currents in it, contraction of the central capsule, changes in the size, position, and form of the pseudopodia, changes in the volume of the calymma (by the evocation of water), &c. Among the sensory functions of the Radiolaria must be especially mentioned their remarkably developed perception of hydrostatic equilibrium (see note F), as well as their perception of distances, so clearly shown in the production of equal lattice-meshes and other regularly formed skeletal structures (see note G).

A. I can add but little to the communication which I made twenty-four years ago regarding sensation in the Radiolaria (L. N. 16, pp. 128-131). The most important point would be the great difference in irritability which must obtain between the pelagic, zonarial and abyssal Radiolaria, which may be assumed from a consideration of their very different conditions of existence as regards pressure, light, warmth, nutrition, &c. It is natural to suppose that the numerous abyssal Radiolaria, discovered by the Challenger, which live at great depths (2000 to 4500 fathoms) in complete darkness, in icy cold and under an enormous pressure, must have quite different sensations of pleasure from their pelagic relatives which live at the surface of the sea under an equatorial sun. Karl Brandt has recently added much to our knowledge regarding the special action of different vital conditions upon the various Polycyttaria and the degrees of their irritability (L. N. 52, pp. 113-132).

B. Regarding the sensation of pressure or sensation of touch of the Radiolaria and the various degrees of their mechanical irritability, see L. N. 16, p. 129; L. N. 41, p. 464.

C. Regarding the sensation of warmth or temperature-sense and its dependence upon different climatic relations, see L. N. 16, p. 129; L. N. 52, pp. 114-129.

D. Regarding the sensation of light, compare L. N. 16, p. 128; L. N. 42, p. 304; L. N. 52, pp. 102-104, 114.

E. Regarding the sense of taste of the Radiolaria or their peculiar sensitiveness towards the different chemical composition of the water, change in its salinity, presence of organic impurities, &c., see L. N. 16, p. 130; L. N. 52, pp. 103, 113. This chemical irritability seems to be the most highly developed sense in the Radiolaria, even more so than their mechanical irritability.

F. The perception of hydrostatic equilibrium among the Radiolaria is immediately visible from the position which their bodies, floating freely in the water, assume spontaneously, and from the symmetrical development of the skeleton, which by its gravitation necessitates a definite position. It may be assumed that the development of the various geometrical ground forms which correspond to a definite position of equilibrium, is the result of this particular kind of perception (compare §§ 40-45).

G. The plastic perception of distance of the pseudopodia is shown by the symmetry with which the forms composing the regular skeletal structures (e.g., the ordinary lattice-spheres with regular hexagonal meshes, the radial spines with equidistant branches) are excreted from the exoplasm. Both this form of sensation and the one first mentioned (note F) have hitherto received scarcely any attention, but are deserving of a thorough physiological investigation.

225. The Cell-Soul (Zellseele).—The common central vital principle, commonly called the "soul," which is considered to be the regulator of all vital functions, appears in the Radiolaria as in other Protista in its simplest form, as the cell-soul. By the continual activity of this central "psyche" all vital functions are maintained in unbroken action, and in uniform correlation. It is also probable that by it the stimulations which the peripheral portions of the cell receive from the outer world are first transmitted into true sensation, and that, on the other hand, the volition, which alone calls forth spontaneous movements, proceeds from it. The central capsule is most likely the sole organ of this cell-soul or central psychic organ, and the active portion may be either the endoplasm or the nucleus, or both. The central capsule may thus (apart from its function as a sporangium, § 215) be regarded as a simple ganglion cell, physiologically comparable to the nervous centre of the higher animals, whilst the exoplasm (sarcomatrix and pseudopodia) are to be compared to the peripheral nervous system and sense organs of the latter. The great simplicity of the functions of the cell-soul which appear in the Radiolaria, and the intimate connection of their different psychic activities, give to these unicellular Protista a special significance for the comprehension of the monistic elements of a natural psychology.

Regarding the theory of the cell-soul as the only psychological theory which is able to explain naturally the true nature of the life of the soul in all organisms as well as in man, see my address on cell-souls and soul-cells ("Zellseelen und Seelenzellen") in Gesammelte populÄre VortrÄge aus dem Gebiete der Entwickelungslehre, Heft 1, p. 143; Bonn, 1878.

CHOROLOGICAL SECTION.

Chapter IX.—GEOGRAPHICAL DISTRIBUTION.

(§§ 226-240.)

226. Universal Marine Distribution.—Radiolaria occur in all the seas of the world, in all climatic zones and at all depths. Probably under normal conditions they always float freely in the water, whether their usual position be at the surface (pelagic), or at a certain depth (zonarial), or near to the bottom of the sea (abyssal). This appears both from numerous direct observations, as well as from conclusions which may be drawn from their organisation (and especially their promorphology) regarding their floating life (compare §§ 40-50, 219, 220). Hitherto no observation has been recorded, which justifies the assumption that Radiolaria live anywhere upon the bottom of the sea (on stones, AlgÆ, or other firm substances), either sessile or creeping. They perform the latter action, however, when they fall accidentally upon a firm basis or are accidentally placed upon it, but they seem normally always to float freely in the water with pseudopodia radiating in all directions. Active free-swimming movements are only met with in the case of the flagellate zoospores (§ 142). The development of Radiolaria in large masses is very remarkable (see note A), and in many parts of the ocean is so great that they play an important part in the economy of marine life, especially as food for other pelagic and abyssal animals (see note B). Medium salinity of the water seems to be most favourable to their development in masses, although it is not unknown in seas of high and low salinity (see note C). There are no Radiolaria in fresh water (see note D).

A. The development of Radiolaria takes place in many parts of the ocean in astonishingly large masses on the surface, in different strata, and near the bottom. The Collodaria (and especially the SphÆrozoida) often cover the surface of the sea in millions, and form a shining layer, phosphorescent in the dark like the NoctilucÆ, as I observed in 1859 in the Strait of Messina, in 1866 at the Canaries, and in 1881 in the Indian Ocean. Similar masses of SphÆrozoum and Acanthometron were seen by Johannes MÜller on the French and Ligurian coasts (L. N. 12), and John Murray found another in the Gulf Stream, off the FÆrÖe Islands, from the surface to a depth of 600 fathoms; considerable masses of large PhÆodaria live there also.

B. The alimentary canal of MedusÆ, SalpÆ, Crustacea, Pteropoda, and many other pelagic animals is a rich field for the discovery of Radiolaria, and many of the species hereinafter described are from such sources. Fossil coprolites too (e.g., those from the Jura) often contain many Polycystina.

C. Some Acantharia (Acanthometra) and PhÆodaria (species of Mesocena and Dictyocha) live in the Baltic; I found their skeletons in the alimentary canal of Aurelia, Ascidians and Copepods.

D. The so-called "fresh-water Radiolaria," which have been described by Focke, Greeff, Grenacher and others, are all Heliozoa, without either central capsule or calymma.

227. Local distribution.—As regards their local distribution and its boundaries the Radiolaria show in general the same relations as other pelagic animals. Since they are only to a very slight extent, if at all, capable of active horizontal locomotion, the dispersion of the different species from their point of development (or "centre of creation") is dependent upon oceanic currents, the play of winds and waves and all the accidental causes which influence the transport of pelagic animals in general. These passive migrations are here, however, as always, of the greatest significance, and bring about the wide distribution of individual species in a far higher degree than any active wanderings could do. Any one who has ever followed a stream of pelagic animals for hours and seen how millions of creatures closely packed together are in a short time carried along for miles by such a current, will be in no danger of underestimating the enormous importance of marine currents in the passive migration of the fauna of the sea. Such constant currents may, however, be recognised both near the bottom of the sea and at various depths, as well as at the surface, and are therefore of just as much significance for the abyssal and zonarial as for the pelagic Radiolaria. It is easy to explain by this means how it is that so many animals of this class (probably indeed the great majority) have a wide range of distribution. The number of cosmopolitan species which live in the Pacific, Atlantic and Indian Oceans is already relatively large. In each of these three great ocean basins, too, many species show a wide distribution. On the other hand, there are very many species which are hitherto known only from one locality, and probably many small local faunas exist, characterised by the special development of particular groups. The observations which we at present possess are too incomplete, and the rich material of the Challenger is too incompletely worked out, to enable any definite conclusions to be drawn regarding the local distribution of Radiolaria.

The statements made in the systematic portion of this Report regarding the distribution of the Challenger Radiolaria are very incomplete. In most cases only one locality is mentioned, and that is the station (§ 240) in the preparations or bottom deposit from which I first found the species in question. Afterwards I often found the same species again in one or more additional stations (not seldom in numerous preparations both from the Pacific and Atlantic), without the possibility of adding them to the habitat recorded under the description. The necessary accurate determination and identification of the species (measuring the different dimensions, counting the pores, &c.), would have occupied too much time, and the writing of this extensive Report would have lasted not ten but twenty or thirty years.

228. Horizontal Distribution.—From the extensive collections of the Challenger and from the other collections which have furnished a welcome supplement to them, it appears that Radiolaria are distributed throughout all seas without distinction of zones and physical conditions, even though these latter may be the cause of differences in their qualitative and quantitative development. In the case of the Radiolaria as well as of many other classes of animals, the law holds good that the richest development of forms and the greatest number of species occurs between the tropics, whilst the frigid zones (both Arctic and Antarctic) exhibit great masses of individuals, but relatively few genera and species (see note A). In the Challenger collection the greatest abundance of species of Radiolaria is exhibited by those preparations which were collected at low latitudes in the immediate neighbourhood of the equator; this is true both of the Atlantic (Stations 346 to 349) and of the Pacific (Stations 266 to 274); in the former the richest of all is Station 347 (lat. 0° 15′ S.), in the latter Station 271 (lat. 0° 33′ S.) (see note B). From the tropics the abundance of species seems to diminish regularly towards the poles, and more rapidly in the northern than in the southern hemisphere; the latter also appears, considered as a whole, to possess more species than the former. A limit to the life of the Radiolaria towards the poles has not yet been found; the expeditions towards the North Pole (see note C), like those towards the South (see note D), have obtained bottom-deposits and ice enclosures which contained Radiolaria; in some of the most northerly and most southerly positions which were reached the number of Radiolaria enclosed in the ice was relatively great.

A. The greater abundance of Radiolaria in the tropical seas is probably to be explained by the more favourable conditions of existence, and in particular the larger quantity of nutritive material (especially of decayed animals) and not by the higher temperature of the surface, for at depths of from 2000 to 3000 fathoms where the abyssal Radiolaria live, the temperature is but little above the freezing point or even below it (compare the bottom temperatures in the list of Challenger Stations, § 240).

B. Station 271 of the Challenger Expedition, situated almost on the equator in the Mid Pacific (lat. 0° 33′ S.), exceeds all other parts of the earth, hitherto known, in respect of its wealth in Radiolaria, and this is true of the pelagic as well as of the zonarial and abyssal forms. In the Station List the deposit at this point is stated to be "Globigerina ooze"; but after the calcareous matter has been removed by means of acid, the purest Radiolarian ooze remains, rich in varied and remarkable species. More than one hundred new species have been described from this Station alone.

C. Regarding the Arctic Radiolaria compare the contributions of Ehrenberg (L. N. 24, pp. 138, 139, 195) and Brady on the English North Polar Expedition, 1875-76 (Ann. and Mag. Nat. Hist., 1878, vol. i. pp. 425, 437).

D. Regarding the Antarctic Radiolaria, compare § 230, note A, and Ehrenberg, Mikrogeologie (L. N. 6, Taf. xxxv., A.), also L. N. 24, pp. 136-139.

229. Fauna of the Pacific Ocean.—From the splendid discoveries of the Challenger, and the supplementary observations obtained from other sources, the Pacific seems to be the ocean basin which is richest both quantitatively and qualitatively in Radiolarian life, excelling both the Indian and Atlantic Oceans in this respect. It may be assumed with great probability that by far the largest portion of the Pacific has a depth of between 2000 and 3000 fathoms, and that its bottom is covered either with Radiolarian ooze (§ 237) or with a red clay (§ 239), which contains many Spumellaria and Nassellaria, and has probably been derived for a great part from broken down and metamorphosed Radiolarian ooze (see note A). Pure Radiolarian ooze was found by the Challenger eastwards in the Central Pacific (over a wide area between lat. 12° N. and 12° S., Stations 265 to 274), and also westwards in the latitude of the Philippines, twenty degrees to the east of them (between lat. 5° N. and 15° N.). The great abundance of Radiolaria present in the neighbourhood of the Philippines and in the Sunda Sea was already known from other investigations (note B). The red clay also, which covers a great part of the bottom of the North Pacific, and which was obtained of very constant composition by the Challenger between lat. 35° N. and 38° N., from Japan to the meridian of Honolulu (from long. 144° E. to 156° W.), is so pre-eminently rich in Radiolaria that it often approaches in composition the Radiolarian ooze, and has probably been derived from it. The track of the Challenger through the tropical and northern parts of the Pacific describes nearly three sides of a rectangle, which includes about half of the enormous Pacific basin, and from this as well as from other supplementary observations it may with great probability be concluded that by far the largest part of the bed of the Pacific (at least three-fourths) is covered either with Radiolarian ooze or with red clay, which contains a larger or smaller amount of the remains of Radiolaria. With this agrees also the important fact that the numerous preparations of pelagic materials and collections of pelagic animals, which were collected by the Challenger in the Pacific, almost always indicate a corresponding amount of Radiolarian life on the surface. This is true in particular also of the South Pacific, between lat. 33° S. and 40° S. (from long. 133° W. to 73° W., Stations 287 to 301); the surface of this southern region and the different bathymetrical zones were rich in new and peculiar species of Radiolaria.

A. Many specimens of bottom-deposits from the Pacific, which are entered in the Challenger lists either as "red clay" or "Globigerina ooze," contain larger or smaller quantities of Radiolaria, and the number of different species of Spumellaria and Nassellaria which they contain is often so great that the deposit might have been almost as appropriately termed "Radiolarian ooze," e.g., Stations 241 to 245, and 270, 271 (compare §§ 236-239).

B. Pacific Radiolarian ooze was first obtained by Lieutenant Brooke (May 11, 1859) between the Philippines and Marianne Islands, from a depth of 3300 fathoms (lat. 18° 3′ N., long. 129° 11′ E.). Ehrenberg, who first described it, found seventy-nine different species of Polycystina in it, and reported "that their quantity and the number of different forms increased with the depth" (Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, 1860, pp. 466, 588, 766).

230. Fauna of the Indian Ocean.—As regards its Radiolarian fauna the Indian Ocean is the least known of the three great basins. Still the few limited spots, regarding which investigations are forthcoming, indicate a very rich development of Radiolarian life. Probably it approaches more nearly the fauna of the Pacific than that of the Atlantic, both as regards the abundance and the morphological characters of its species. The researches of the Challenger are very limited and incomplete as regards the Indian Ocean, for the expedition only just touched upon this great ocean basin (2000 to 3000 fathoms deep) at its two extremities (westwards at the Cape of Good Hope and eastwards at Tasmania), its course lying for the most part south of lat. 45° S. and extending beyond lat. 65° S. (from Station 149 to 158, south of lat. 50° S.). It is true that this portion of the South Indian Ocean was shown to contain Radiolaria everywhere, but these were more plentiful in individuals than in species. Only from Station 156 to Station 159 (between lat. 62° and 47° S., and long. 95° and 130° E.) was the bottom, which consisted partly of Diatom ooze and partly of Globigerina ooze, richer in species (see note A). The gaps left by the Challenger in the investigation of the Indian Ocean, have, however, been to some extent filled from other sources. As early as 1859 the English "Cyclops" expedition had shown that the bottom of the Indian Ocean to the east of Zanzibar (lat. 9° 37′ S., long. 61° 33′ W.) is covered with pure Radiolarian ooze (see note B). Also since the Tertiary rocks of the Nicobar Islands are for the most part of the same composition, and since a great abundance of Radiolaria has been shown to be present both in the east part of the ocean, between the Cocos Islands and the Sunda Archipelago (see note C), and in the northern part or Arabian Sea between Socotra and Ceylon (see note D); it may be assumed with great probability that the greater part of the basin of the Indian Ocean, like that of the Pacific, is covered either with Radiolarian ooze or with the characteristic red clay. With this agrees the richness of the surface of the Indian Ocean in Radiolaria of the most various groups, which has been more extensively demonstrated.

A. The Radiolarian fauna collected by the Challenger on the voyage from the Cape to Melbourne, shows in part, namely, from Station 156 to Station 158, very peculiar and characteristic composition; in particular, the Diatom ooze of Station 157 passes over in great part into a Radiolarian ooze, mainly composed of SphÆrellaria. This is worthy of a more thorough investigation than I was able, owing to lack of material and time, to give it.

B. The remarkably pure Radiolarian ooze of Zanzibar, discovered by Ehrenberg in 1859, was the earliest known recent example of that deposit. It was brought up by Captain Pullen of the English man-of-war "Cyclops," from a depth of 2200 fathoms, between Zanzibar and the Seychelles, and "under a magnifying power of 300 diameters, showed at the first glance a mass of almost pure Polycystina, such as no sample of a deep-sea deposit has hitherto shown. It is very noticeable that in the whole of this mass of living forms, no calcareous shells are to be seen" (Ehrenberg, L. N. 24, pp. 148, 149).

C. For the most important material from the Indian Ocean, I am indebted to Captain Heinrich Rabbe of Bremen, who during many voyages in the Indian Ocean, in his ship "Joseph Haydn," made numerous collections in different localities with the tow-net and the trawl, and admirably preserved the rich collections thus made. The greatest abundance of Radiolaria was found in those obtained to the east of Madagascar, and next in those from the neighbourhood of the Cocos Islands. I take this opportunity of expressing my thanks to Captain Rabbe for the liberality with which he placed all this valuable material at my disposal.

D. On my voyage from Aden to Bombay, and thence to Ceylon (1881), and especially on my return journey from Ceylon, between the Maldive Islands and Socotra (1882), I carried on a number of experiments with a surface net, which yielded a rich fauna of pelagic animals, and among them many new species of Radiolaria, for observation. On several nights when the smooth surface of the Indian Ocean, unrippled by any wind, shone with the most lovely phosphorescent light, I drew up water from the surface with a bucket, and obtained a rich booty. A number of other new species of Radiolaria from very various parts of the Indian Ocean I obtained from the alimentary canal of pelagic animals, such as MedusÆ, SalpÆ, Crustacea, &c. Although the total number of Radiolaria known to me from the Indian Ocean is much less than from the Atlantic and Pacific, there are several new genera and numerous species among them, which show that a careful study of this fauna will be of wide interest.

231. Fauna of the Atlantic Ocean.—The Atlantic Ocean in all parts, of which the pelagic fauna has been examined, has shown the same constant presence of Radiolaria, and in certain parts of its abyssal deposits a larger or smaller quantity of different types belonging to this class; on the whole, however, its Radiolarian fauna is inferior to that of the Pacific, and probably also to that of the Indian Ocean, both in quantity and quality. Pure Radiolarian ooze, such as is so extensively found on the floor of the Pacific, and in certain places in that of the Indian Ocean, has not yet been found in the Atlantic (see § 237). The red clay, too, of the deep Atlantic does not seem to be so rich in Radiolaria as that of the Pacific; nevertheless, the number of species peculiar to the Atlantic is very large, and at certain points the abundance of species as well as of individuals seems to be scarcely less than in the Pacific. This is especially true of the eastern equatorial zone not far from Sierra Leone, Stations 347 to 352 (see note A); also of the South Atlantic between Buenos Ayres and Tristan da Cunha, Stations 324, 325, 331 to 333 (see note B); and, lastly, in the North Atlantic in the Gulf Stream and near the Canary Islands (see note C). The fauna of the latter agrees for the most part with that of the Mediterranean (see note D). In addition to the material collected by the Challenger, other deep-sea investigations have furnished bottom-deposits from different parts of the ocean, which have proved very rich in Radiolaria (see note E). Furthermore, since the island of Barbados consists for the most part of fossil Radiolarian ooze, it is very probable that at certain parts of the tropical Atlantic true Radiolarian ooze, like that of the Pacific and Indian Oceans, will eventually be found in depths between 2000 and 3000 fathoms, perhaps over a considerable area.

A. The tropical zone of the eastern Atlantic seems to be especially rich in peculiar Radiolaria of different species. This is shown by numerous preparations from the surface, and from various depths (between lat. 3° S. and 11° N., and long. 14° W. to 18° W.), which were made towards the end of the cruise. Unfortunately no bottom-deposits were obtained from the most important stations (except Nos. 346 and 347, depths 2350 and 2250 fathoms) in this region; at these the deposit was a Globigerina ooze containing numerous different species of Radiolaria.

B. In the South Atlantic, between Buenos Ayres and Tristan da Cunha (between lat. 35° S. and 43° S., long. 8° W. and 57° W.) there appears to be a long stretch covered partly with Globigerina ooze (Stations 331 to 334), or red clay (Stations 329, 330), partly with blue mud (Stations 318 to 328), which contains not only large masses of individuals but numerous peculiar species of Spumellaria and Nassellaria. The preparations from the surface-takings of this region are also rich in these, as well as in peculiar PhÆodaria.

C. The northern part of the Atlantic appears on the whole to be inferior to the tropical and southern portions as regards its richness in Radiolaria, and from the western half more especially, only few species are known. From my researches at Lanzerote in 1866-67, it appears that the pelagic fauna of the Canary Islands is very rich in them, as is also the Gulf Stream in the neighbourhood of the FÆrÖe Channel, according to the investigations of John Murray (see his Report on the "Knight-Errant" Expedition, Proc. Roy. Soc. Edin., vol. xi., 1882).

D. The Radiolaria of the Mediterranean are of special interest, because almost all our knowledge of these organisms in the living conditions and of their vital functions has been derived from investigations conducted on its shores. Johannes MÜller laid the foundation of this knowledge by his investigations at Messina, and on the Ligurian and French coasts at Nice, Cette, and St. Tropez (L. N. 10). The many new Radiolaria which I described in my Monograph (L. N. 16, 1862), were for the most part taken at Messina, the place which possesses a richer pelagic fauna than any other, so far as is yet known, in the Mediterranean. Other new species I found afterwards at Villafranca near Nice, in 1864 (L. N. 19), at Portofino near Genoa (1880), at Corfu (1877), and at other points on the coast. In Messina also, Richard Hertwig collected the material for his valuable treatise on the Organisation of the Radiolaria (L. N. 33), after he had previously made investigations into their histology at Ajaccio in Corsica (L. N. 26). Lastly, at Naples, Cienkowski (L. N. 22) and Karl Brandt (L. N. 38, 39, 52) carried out their important investigations into the reproduction and symbiosis of the Radiolaria. With respect to the character of its Radiolaria, the Mediterranean fauna is to be regarded as a special province of the North Atlantic.

E. Among the smaller contributions which have been made towards our knowledge of the Atlantic Radiolarian fauna, the communications of Ehrenberg on the deposits obtained in sounding for the Atlantic cable, and on the Mexican Gulf Stream near Florida, deserve special mention (L. N. 24, pp. 138, 139-145).

232. Vertical Distribution.—The most important general result of the discoveries of the Challenger, as regards the vertical or bathymetrical distribution of the Radiolaria, is the interesting fact that numerous species of this class are found living at the most various depths of the sea, and that certain species are limited to particular bathymetrical zones, i.e., are adapted to the conditions which obtain there. In this respect three different Radiolarian faunas may be distinguished, which may be shortly termed "pelagic," "zonarial," and "abyssal." The pelagic Radiolaria swim at the surface, and when they sink (e.g., in a stormy sea), only descend to a small depth, probably not more than from 20 to 30 fathoms (§ 233). The complicated conditions of existence created by the keen struggle for existence at the surface of the sea, give rise to the formation of very numerous pelagic species, especially of Porulosa (Spumellaria and Acantharia). The abyssal Radiolaria are very different from those just mentioned; they live at the bottom of the deep-sea, not resting upon nor attached to it, but probably floating at a little distance above it, and are adapted to the conditions of existence which obtain there (§ 235). Here the Osculosa (Nassellaria and PhÆodaria) seem to predominate. The zonarial Radiolaria live floating at various depths between the pelagic and abyssal species (§ 234). In their morphological characters they gradually approach the pelagic forms upwards and the abyssal downwards.

The views which have hitherto been held regarding the bathymetrical or vertical distribution of the Radiolaria have been entirely altered by the magnificent discoveries of the Challenger, and especially by the important observations of Sir Wyville Thomson (L. N. 31) and John Murray (L. N. 27). These two distinguished deep-sea explorers have, as a result of their wide experience, been convinced that Radiolaria exist at all depths of the ocean, and that there are large numbers of true deep-sea species which are never found at the surface of the sea nor at slight depths (L. N. 31, vol. i. pp. 236-238; L. N. 27, pp. 523, 525). The result of my ten years' work upon the Challenger Radiolaria, and the comparative study of more than a thousand mountings from all depths, has only been to confirm this opinion, and I am further persuaded that it will some day be possible by the aid of suitable nets (not yet invented) to distinguish different faunistic zones in the various depths of the sea. In this connection may be mentioned the specially interesting fact that the species of Radiolaria of one and the same family present in the different depths characteristic morphological distinctions, which obviously correspond to their different physiological relations in the struggle for existence. Owing to those extensive discoveries, the representation which I gave in my Monograph (1862, L. N. 16, pp. 172-196) of the vertical distribution of the Radiolaria, and of their life in the greatest depths of the sea, has been entirely changed. Compare also BÜtschli (L. N. 41, p. 466).

233. The Pelagic Fauna.—The surface of the open ocean seems everywhere, at a certain distance from the coast at least, to be peopled by crowds of living Radiolaria. In the tropical zone these pelagic crowds consist of many different species, whilst in the frigid zones, on the other hand, they are made up of many individuals belonging to but few species. Most of these inhabitants of the surface may be regarded as truly pelagic species, which either remain always at the surface or descend only very slightly below it. Probably most Porulosa (both Spumellaria and Acantharia) belong to this group; whilst but few Osculosa occur in it, and fewer PhÆodaria than Nassellaria. In general the pelagic Radiolaria are distinguished from the abyssal by the more delicate and slender structure of their skeletons; the pores of the lattice-shells are larger, the intervening trabeculÆ thinner; the armature of spines, spathillÆ, anchors, &c., is more various and more highly developed. Numerous forms are to be found among the pelagic Radiolaria which have either an incomplete skeleton or none at all. When the pelagic forms leave the surface on account of unfavourable weather, they appear only to sink to slight depths (probably not below 20 or 30 fathoms). Within the limits of the same family the size of the pelagic species seems to be on an average greater than that of the related abyssal forms.

234. The Zonarial Fauna.—Between the pelagic fauna living at the surface of the open sea and the abyssal, which floats immediately over the bottom, there appears to be usually a middle fauna, which inhabits the different bathymetrical zones of the intermediate water, and hence may be shortly called the "zonarial" fauna. The different species of Radiolaria which inhabit these different strata in the same vertical column of water present differences corresponding to those of the plants composing the several zones of vegetation, which succeed each other at different heights on a mountain; they correspond to the different conditions of existence which are presented by the different strata of water, and to which they have become adapted in the struggle for existence. The existence of such bathymetrical zones has been shown by those important, if not numerous, observations of the Challenger, in which the tow-net was used at different depths at one and the same Station. In several cases the character of the Radiolarian fauna at different depths presented characteristic differences.

For the present, and until we are better acquainted with the characters of the Radiolarian fauna at different depths, we may distinguish provisionally the following five bathymetrical zones:—(1) The pelagic zone, extending from the surface to a depth of about 25 fathoms; (2) the pellucid zone, extending from 25 to 150 fathoms, or as far as the influence of the sunlight makes itself felt; (3) the obscure zone, extending from 150 to 2000 fathoms, or from the depth at which sunlight disappears to that at which the influence of the water containing carbonic acid begins and the calcareous organisms vanish; (4) the siliceous zone, extending from 2000 or 2500 to about 3000 fathoms, in which only siliceous not calcareous Rhizopoda are found, and in which the peculiar conditions of the lowest regions have not yet appeared; (5) the abyssal zone, in which the accumulation of the oceanic deposits, and the influence of the bottom currents, create new conditions of existence. So far as our isolated and incomplete observations of the zonarial Radiolarian fauna extend, it appears that the subclass Porulosa (Spumellaria and Acantharia) predominates in the two upper zones, and as the depth increases is gradually replaced by the subclass Osculosa (Nassellaria and PhÆodaria), so that the latter predominates in the two lowest zones. The obscure zone which lies in the middle is probably the poorest in species. In general, the morphological characters of the zonarial fauna appear to change gradually upwards into the delicate form of the pelagic and downwards into the robust constitution of the abyssal; so also the average size of the individuals (within the limits of the same family) appears to increase upwards and decrease downwards.

235. The Abyssal Fauna.—The great majority of Radiolaria which have hitherto been observed, and which are described in the systematic portion of this Report, have been obtained from the bottom of the deep-sea, and more than half of all the species have been derived from the pure Radiolarian ooze, which forms the bed of the Central Pacific at depths of from 2000 to 4000 fathoms (§ 237). Many of these abyssal forms were brought up with the malacoma uninjured, and they show, both when mounted immediately in balsam, and when preserved in alcohol, all the soft parts almost as clearly as fresh preparations of pelagic Radiolaria. These species are to be regarded as truly abyssal, i.e., as forms which live floating only a little distance above the bottom of the deep-sea, having become adapted to the peculiar conditions of life which obtain in the lowest regions of the ocean. Probably the majority of the PhÆodaria belong to these abyssal Radiolaria, as well as a large number of Nassellaria, but on the other hand, only a small number of Acantharia and Spumellaria are found there. A character common to these abyssal forms, and rarely found in those from the surface or from slight depths, is found in their small size and their heavy massive skeletons, in which they strikingly resemble the fossil Radiolaria of Barbados and the Nicobar Islands. The lattice-work of the shell is coarser, its trabeculÆ thicker and its pores smaller than in pelagic species of the same group; also the apophyses (spines, spathillÆ, coronets, &c.), are much less developed than in the latter. From these true abyssal Radiolaria must be carefully distinguished those species whose empty skeletons, devoid of all soft parts, occur also in the Radiolarian ooze of the deep-sea, but are clearly only the sunken remains of dead forms, which have lived at the surface or in some of the upper zones.

236. Deposits containing Radiolaria.—The richest collection of Radiolaria is found in the deposits of ooze which form the bed of the ocean. Although the pelagic material skimmed from the surface of the sea, and the zonarial material taken by sinking the tow-net to various depths, are always more or less rich in Radiolaria, still the number of species thus obtained is, on the whole, much less than has hitherto been got merely from deep-sea deposits. Of course the skeletons found in the mud of the ocean-bed, may belong either to the abyssal species which live there (§ 235), or to the zonarial (§ 234), or to the pelagic species (§ 233), for the siliceous skeletons of these latter sink to the bottom after their death. Almost all these remains found in the deposits belong to the siliceous "Polycystina" (Spumellaria and Nassellaria); PhÆodaria occur but sparingly, and Acantharia are entirely wanting, for their acanthin skeleton readily dissolves. The abundance of Radiolaria varies greatly according to the composition and origin of the deposits. In general marine deposits may be divided into two main divisions, terrigenous and abyssal, or, more shortly, muds and oozes. The terrigenous deposits (or muds) include all those sediments which are made up for the most part of materials worn away from the coasts of continents and islands, or brought down into the sea by rivers. Their greatest extent from the coast is about 200 nautical miles. They contain varying quantities of Radiolaria, but much fewer than those of the next group. The abyssal deposits (or oozes) usually commence at a distance of from 100 to 200 nautical miles from the coast. In general they are characterised by great uniformity, corresponding to the constancy of the conditions under which they are laid down; they may be divided into three categories, the true Radiolarian ooze (§ 237), Globigerina ooze (§ 238), and red clay (§ 239). Of these three most important deep-sea formations the first is by far the richest in Radiolaria, although the other two contain often very many siliceous shells.

The marvellous discoveries of the Challenger have thrown upon the nature of marine deposits an entirely new light, which justifies most important conclusions regarding the geographical distribution and geological significance of the Radiolaria. Since Dr. John Murray and the AbbÉ Renard will treat fully of these interesting relations in a forthcoming volume of the Challenger series (Report on the Deep-Sea Deposits), it will be sufficient here to refer to their preliminary publication already published (Narrative of the Cruise of H.M.S. Challenger, 1885, vol. ii. part ii. pp. 915-926); see also the earlier communications by John Murray (1876, L. N. 27, pp. 518-537), and by Sir Wyville Thomson (The Atlantic, L. N. 31, vol. i. pp. 206-246). In the Narrative (loc. cit., p. 916) the following table of marine deposits is given:—

Terrigenous deposits. brace Shore formations, brace Found in inland seas and along the shores of continents.
Blue mud,
Green mud and sand,
Red mud,
 
Volcanic mud and sand, brace Found around oceanic islands and along the shores of continents.
Coral mud and sand,
Coralline mud and sand,
 
Abysmal deposits. brace Globigerina ooze, brace Found in the abysmal regions of the ocean basins.
Pteropod ooze,
Diatom ooze,
Radiolarian ooze,
Red clay,

237. Radiolarian Ooze.—By Radiolarian ooze, in the strict sense of the term, are understood those oceanic deposits, the greater part of which (often more than three-quarters) is composed of the siliceous skeletons of this class. Such pure Radiolarian ooze has only been found in limited areas of the Pacific and Indian Oceans. It is most conspicuous in the Central Pacific, between lat. 12° N. and 8° S., long. 148° W. to 152° W., the depth being everywhere between 2000 and 3000 fathoms (Stations 266 to 268 and 272 to 274). In the deepest of the Challenger soundings (Station 225, 4475 fathoms) the bottom is composed of pure Radiolarian ooze, as well as at the next Station in the Western Tropical Pacific (Station 226, 2300 fathoms), the latitude varying from 12° N. to 15° N., and the longitude from 142° E. to 144° E. In the Indian Ocean also, pure Radiolarian ooze was found in the year 1859 between Zanzibar and the Seychelles, this being the first known example of it (§ 230). On the other hand, it has not yet been found in the bed of the Atlantic; but the Tertiary formations of Barbados (Antilles, § 231) like those of the Nicobar Islands (Further India), are to be regarded as pure Radiolarian ooze in the fossil condition. Mixed Radiolarian ooze is the name given to those deposits in which the Radiolaria exceed any of the other organic constituents, although they do not make up half the total mass. To this category belong a large number of the Challenger soundings which are entered in the Station list either as red clay or Globigerina ooze. Such mixed Radiolarian ooze has been discovered (A) in the North Pacific in an elongated area of red clay extending from Station 241 to Station 245 (perhaps even from Station 238 to Station 253), that is, at least, from long. 157° E. to 175° E., between lat. 35° N. and 37° N.; (B) in the tropical Central Pacific in the Globigerina ooze of Stations 270 and 271. The ooze from the latter station, situated almost on the equator (lat. 0° 33′ S., long. 151° 34′ W.), is specially remarkable, for it has yielded more new species of Spumellaria and Nassellaria than any other Station, not excluding even the neighbouring Stations 268, 269, and 272. Probably such mixed Radiolarian ooze is very widely distributed in the depths of the ocean, as, for example, in the South Pacific (Stations 288, 289, 300, and 302), and in the Southern Ocean (Stations 156 to 159); also in the South Atlantic (Stations 324, 325, 331, 332) and in the tropical Atlantic (Stations 348 to 352). When carefully purified and decalcified by acids, Radiolarian ooze appears as a fine shining white powder; in the raw state it is yellowish or reddish, sometimes reddish-brown or dark brown in colour, according to the quantity of oxides of iron, manganese, &c., which it contains. Calcareous skeletons (especially the tests of pelagic Foraminifera) do not occur at all or only in very minute quantities in pure Radiolarian ooze from more than 2000 fathoms, whilst specimens of mixed ooze often contain considerable quantities of them.

Pure Radiolarian ooze was first described by Dr. John Murray as regards its peculiar nature and composition under the name "Radiolarian ooze" (1876, L. N. 27, pp. 525, 526); compare also Sir Wyville Thomson (The Atlantic, L. N. 31, vol. i. pp. 231-238), and John Murray (Narr. Chall. Exp., L. N. 53, vol. i. pt. ii. pp. 920-926, pl. N. fig. 2). The different specimens of pure Radiolarian ooze obtained by the Challenger from the Pacific, and handed to me for investigation, are from depths of from 2250 fathoms to 4475 fathoms, and may be divided according to their composition into three different groups:—I. The Radiolarian ooze of the Western Tropical Pacific, Stations 225 and 226, from depths of 4475 and 2300 fathoms (lat. 11° N. to 15° N., and long. 142° E. to 144° E.). II. The Radiolarian ooze of the northern half of the Central Pacific, Stations 265 to 269, from depths of 2550 to 2900 fathoms. III. The Radiolarian ooze of the southern half of the Central Pacific, Stations 270 to 274, from depths of 2350 to 2925 fathoms. A fourth group would be constituted by the Radiolarian ooze from the Philippines, which was brought up by Brooke in 1860 near the Marianne Islands from 3300 fathoms, and described by Ehrenberg (Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, 1860, p. 765). The Diatom ooze, too, found by the Challenger in the Antarctic regions (Stations 152 to 157) is in some parts so rich in Radiolaria that it passes over into true Radiolarian ooze. Regarding the Radiolarian ooze from Zanzibar, obtained by Captain Pullen in 1859 from 2200 fathoms (§ 230), we have only the incomplete communications of Ehrenberg (L. N. 24, p. 147). A more accurate knowledge of these deposits from the Indian Ocean, and of those which we may with probability expect from the tropical eastern Atlantic, will be sure to increase very widely our knowledge of the class.

238. Globigerina Ooze.—Next to the Radiolarian ooze proper the Globigerina ooze is the deposit which is richest in the remains of Radiolaria. Often these are so abundant that it is doubtful to which category the specimen should be referred (e.g., Stations 270 and 271, see § 237). In fact, the two pass without any sharp boundary into each other, and both present transitions to the Diatom ooze. Next to red clay (§ 239), Globigerina ooze is the most widely distributed of all sediments, and forms a large part of the bed of the ocean at depths of 250 to 2900 fathoms (especially between 1000 and 2000 fathoms). It covers extensive areas at depths below 1800 fathoms, and in still deeper water is replaced by red clay. It is a fine-grained white, grey, or yellowish powder, which sometimes becomes coloured rose, red, or brown owing to the admixture of oxides of iron and manganese. True Globigerina ooze consists for the most part of the accumulated calcareous shells of pelagic Foraminifera, principally Globigerina and Orbulina, but also Hastigerina, Pulvinulina, &c. It contains usually from 50 to 80 per cent. of calcium carbonate, the extreme values being 40 and 95 per cent. After this has been removed by acids, there remains a residue, which consists partly of the siliceous shells of Radiolaria and Diatoms, and partly of mineral particles identical with the volcanic elements of the red clay.

Regarding the composition and significance of the Globigerina ooze, see John Murray (L. N. 27, pp. 523-525, and L. N. 53, vol. i. p. 919). Recently this author has separated from the Globigerina ooze (sensu stricto), the Pteropod ooze, distinguished from the former by the greater abundance of Pteropod shells and calcareous shells of larger pelagic organisms which it contains. It is found in moderate depths (at most 1500 fathoms), and contains fewer Radiolaria.

239. Red Clay.—This is quantitatively the most important of all deep-sea deposits, covering by far the greatest extent of the three great ocean basins at depths greater than 2200 fathoms. It thus far surpasses in area the other deposits, both Radiolaria and Globigerina oozes, and commonly forms a still deeper layer beneath them. Probably these three deep-sea deposits together cover about three-eighths of the whole surface of the earth, that is, about as much as all the continents together, whilst only two-eighths are covered by the terrigenous deposits. Red clay is principally composed of silicate of alumina, mixed in various proportions with other finely granular substances; its usual red colour, which sometimes passes over into grey or brown, is more especially due to admixture of oxides of iron and manganese. Calcareous matter is usually entirely wanting, or present only in traces, whilst free silica is found in very variable, often considerable quantities. The chief mass of the red clay consists of volcanic ashes, pumice, fragments of lava, &c., whilst a large part of it is generally composed of shells of Radiolaria or fragments of them; in many places the number of well-preserved skeletons contained in the red clay is very considerable, so that it passes over gradually into the Radiolarian ooze (e.g., in the North Pacific, Stations 238 to 253, see § 237). Hence it may be supposed that a large part of the red clay consists of decomposed Radiolarian ooze.

The characteristic composition and fundamental significance of the red clay in the formation of the deep-sea bed were first made known by the discoveries of the Challenger (compare John Murray, 1876, L. N. 27, p. 527, and Narr. Chall. Exp., L. N. 53, vol. i. pt. ii. pp. 920-926, pl. N; also Wyville Thomson, The Atlantic, L. N. 31, vol. i. pp. 226-229). The mineral components of the red clay are for the most part of volcanic origin, due to the decomposition of pumice, lava, &c. Among the organic remains found in it, the siliceous skeletons of Radiolaria are by far the most important, and their number is often considerable. A large portion of the red clay appears to me to consist of broken down Radiolarian shells, in which a peculiar metamorphism probably has taken place. Sir Wyville Thomson was of opinion that a considerable proportion of it consisted of the remains of Globigerina ooze, the calcareous constituents of which had been removed by the carbon dioxide in the deep-sea water (L. N. 31, loc. cit.). Among these remains, however, the siliceous skeletons of the Radiolaria play a significant and often the most important part. Furthermore, John Murray has called attention to the fact that in many deep-sea deposits yellow and red insoluble particles remain, which unmistakably present the form of Radiolarian shells (L. N. 27, p. 513). At Station 303 he found "amorphous clayey matter, rounded yellow minerals, many Radiolaria-shaped;" at Station 302 there was sediment "consisting almost entirely of small rounded red mineral particles; many of these had the form of both Foraminifera and Radiolaria; and it seemed as if some substance had been deposited in and on these organisms." Similar transitions from well-preserved Radiolarian shells into amorphous mineral particles I have found in several other specimens of Challenger soundings, and consider them a further argument for the supposition that the Radiolaria often take an important share in the formation of the red clay.

240. List of Stations at which Radiolaria were observed on the Challenger Expedition.—The 168 Stations recorded below, in soundings or surface preparations from which I found Radiolaria, belong to the most various parts of the sea which the Challenger traversed during her voyage round the world; they constitute about half of the (364) observing Stations contained in the official list published in the Narrative of the Cruise (Narr. Chall. Exp., vol. i. part ii. Appendix ii.).

In addition to the particulars given in the list regarding the geographical position of the Station, depth, temperature, and composition of the bottom deposit, I have added the result of my investigations as regards the relative abundance of the Radiolaria in each. The five letters (A to E) denote the following degrees of frequency:—A, abundant Radiolaria (AI, pure Radiolarian ooze; AII, mixed Radiolarian ooze); B, very numerous Radiolaria (but not a predominating quantity); C, many Radiolaria (medium quantity); D, few Radiolaria; E, very few Radiolaria (as they occur almost always). In using these symbols regard has been had to abundance of the abyssal as well as of the zonarial and pelagic forms (§ 232); sometimes also the estimated number of Radiolaria has been inserted, based upon information given by John Murray in his Preliminary Report (L. N. 27), and in the Narrative of the Cruise (L. N. 53), as well as by Henry B. Brady in his Report on the Foraminifera (Zool. Chall. Exp., part xxii., 1884). From Stations 348 to 352 in the Eastern Tropical Atlantic no specimens of the bottom were obtained, but a rich pelagic Radiolarian fauna was demonstrated by numerous preparations from the surface. The depths are given in fathoms and the temperature in degrees Fahrenheit. In the column describing the nature of the bottom the following abbreviations are used:—

rad. oz. = Radiolarian ooze (§ 237).
gl. oz. = Globigerina ooze (§ 238).
r. cl. = red clay (§ 239).
pt. oz. = Pteropod ooze (see p. clviii).
di. oz. = Diatom ooze (see p. clvii).		 bl. m. = blue mud,
gr. m. = green mud,
volc. m. = volcanic mud,		 brace terrigenous deposits
(see p. clvi).
r. m. = red mud.
 
rad. oz. = Radiolarian ooze (§ 237).
gl. oz. = Globigerina ooze (§ 238).
r. cl. = red clay (§ 239).
pt. oz. = Pteropod ooze (see p. clviii).
di. oz. = Diatom ooze (see p. clvii).
bl. m. = blue mud, brace terrigenous deposits
(see p. clvi).
gr. m. = green mud,
volc. m. = volcanic mud,
r. m. = red mud.
Challenger Station Locality 1. Depth in Fathoms Bottom Temperature °F Nature of Bottom Relative
Abundance of
Radiolaria.		 Date. Latitude and Longitude. Nearest Land.
1873.
001. N. Atl. 1890 36.8 gl. oz. D few Feb. 15 27° 24′ N., 16° 55′ W. S. of Tenerife.
002. N. " 1945 36.8 gl. oz. E very few F" 17 25° 52′ N., 19° 22′ W. S.W. of the Canary Islands.
005. N. " 2740 37.0 r. cl. D few F" 21 24° 20′ N., 24° 28′ W. S.W. of the Canary Islands.
009. N. " 3150 36.8 r. cl. E very few F" 26 23° 23′ N., 35° 11′ W.  (Ocean).
024. Tr. Atl. 390 ... pt. oz. D few Mar. 25 18° 38′ N., 65° 5′ W. Culebra (Antilles).
 
032. N. Atl. 2250 36.7 gl. oz. E very few April 3 31° 49′ N., 64° 55′ W. Bermuda.
045. N. " 1240 37.2 bl. m. E very" May 3 38° 34′ N., 72° 10′ W. S. of New York.
050. N. " 1250 38.0 bl. m. E very" F" 21 42° 8′ N., 63° 39′ W. S. of Halifax.
064. N. " 2700 ... r. cl. D few June 20 35° 35′ N., 50° 27′ W.  (Ocean).
076. N. " 900 40.0 pt. oz. D f" July 3 38° 11′ N., 27° 9′ W. Azores.
 
098. Tr. Atl. 1750 36.7 gl. oz. C many Aug. 14 9° 21′ N., 18° 28′ W. W. of Sierra Leone.
106. Tr. " 1850 36.6 gl. oz. C m" F" 25 1° 47′ N., 24° 26′ W.  (Ocean).
108. Tr. " 1900 36.8 gl. oz. C m" F" 27 1° 10′ N., 28° 23′ W.  (Ocean).
111. Tr. " 2475 33.7 gl. oz. C m" F" 31 1° 45′ S., 30° 58′ W.  (Ocean).
120. Tr. " 675 ... r. m. D few Sept. 9 8° 37′ S., 34° 28′ W. Pernambuco.
 
132. S. Atl. 2050 35.0 gl. oz. C many Oct. 10 35° 25′ S., 23° 40′ W. Tristan da Cunha.
134. S. " 2025 36.0 gl. oz. C m" F" 14 36° 12′ S., 12° 16′ W. Tristan da Cunha.
137. S. " 2550 34.5 r. cl. D few F" 23 35° 59′ S., 1° 34′ E.  (Ocean).
138. S. " 2650 35.1 r. cl. D f" F" 25 36° 22′ S., 8° 12′ E.  (Ocean).
143. S. Ind. 1900 35.6 gl. oz. E very few Dec. 19 36° 48′ S., 19° 24′ E. Cape of Good Hope.
 
144. S. " 1570 35.8 gl. oz. E very" F" 24 45° 57′ S., 34° 39′ E.  (Ocean).
145. S. " 140 ... volc. s. D few F" 27 46° 43′ S., 38° 4′ E. Prince Edward Island.
146. S. " 1375 35.6 gl. oz. C many F" 29 46° 46′ S., 45° 31′ E.  (Ocean).
147. S. " 1600 34.2 di. oz. C m" F" 30 46° 16′ S., 48° 27′ E. W. of the Crozet Islands.
1874.
148. S. " 210 ... gravel,
 shells		 D few Jan. 3 46° 47′ S., 51° 37′ E. E. of the Crozet Islands.
 
149H. S. " 127 ... volc. m. D f" F" 29 48° 45′ S., 69° 14′ E. Kerguelen Island.
150. S. " 150 35.2 gravel D f" Feb. 2 52° 4′ S., 71° 22′ E. N. of Heard Island.
151. S. " 75 ... volc. m. D f" F" 7 52° 59′ S., 73° 33′ E. Heard Island.
152. S. " 1260 ... di. oz. C many F" 11 60° 52′ S., 80° 20′ E.  (Ocean).
153. S. " 1675 ... bl. m. C m" F" 14 65° 42′ S., 79° 49′ E. Antarctic Ice.
 
154. S. " 1800 ... bl. m. C m" F" 19 64° 37′ S., 85° 49′ E. Antarctic Ice.
155. S. " 1300 ... bl. m. C m" F" 23 64° 18′ S., 94° 47′ E. Antarctic Ice.
156. S. " 1975 ... di. oz. B numerous F" 26 62° 26′ S., 95° 44′ E.  (Ocean).
157. S. " 1950 32.1 di. oz. B num" Mar. 3 53° 55′ S., 108° 35′ E.  (Ocean).
158. S. " 1800 33.5 gl. oz. B num" F" 7 50° 1′ S., 123° 4′ E.  (Ocean).
 
159. S. " 2150 34.5 gl. oz. B num" F" 10 47° 25′ S., 130° 22′ E.  (Ocean).
160. S. " 2600 33.9 r. cl. C many F" 13 42° 42′ S., 134° 10′ E.  (Ocean).
162. S. " 38 ... sand E very few April 2 39° 10′ S., 146° 37′ E. Bass Strait.
163. S. Pac. 2200 34.5 gr. m. E very" F" 4 36° 57′ S., 150° 34′ E. Port Jackson.
164A. S. " 1200 ... gr. m. E very" June 13 34° 9′ S., 151° 55′ E. W. of Sydney.
Challenger Station Locality 2. Depth in Fathoms Bottom Temperature °F Nature of Bottom Relative
Abundance of
Radiolaria.
001. N. Atl. 1890 36.8 gl. oz. D few
002. N. " 1945 36.8 gl. oz. E very few
005. N. " 2740 37.0 r. cl. D few
009. N. " 3150 36.8 r. cl. E very few
024. Tr. Atl. 390 ... pt. oz. D few
 
032. N. Atl. 2250 36.7 gl. oz. E very few
045. N. " 1240 37.2 bl. m. E very"
050. N. " 1250 38.0 bl. m. E very"
064. N. " 2700 ... r. cl. D few
076. N. " 900 40.0 pt. oz. D f"
 
098. Tr. Atl. 1750 36.7 gl. oz. C many
106. Tr. " 1850 36.6 gl. oz. C m"
108. Tr. " 1900 36.8 gl. oz. C m"
111. Tr. " 2475 33.7 gl. oz. C m"
120. Tr. " 675 ... r. m. D few
 
132. S. Atl. 2050 35.0 gl. oz. C many
134. S. " 2025 36.0 gl. oz. C m"
137. S. " 2550 34.5 r. cl. D few
138. S. " 2650 35.1 r. cl. D f"
143. S. Ind. 1900 35.6 gl. oz. E very few
 
144. S. " 1570 35.8 gl. oz. E very"
145. S. " 140 ... volc. s. D few
146. S. " 1375 35.6<

241. Historical Distribution.—Radiolaria are found fossil in all the more important groups of the sedimentary rocks of the earth's crust. Whilst a few years ago their well-preserved siliceous skeletons were only known in considerable quantity from Cainozoic marls (§ 242), very many Spumellaria and Nassellaria have recently been found in Mesozoic and a few in PalÆozoic strata. By the aid of improved modern methods of investigation (especially by the preparation of thin sections of very hard rocks) it has been shown that many hard siliceous minerals, especially cryptocrystalline quartz, contain numerous well-preserved Radiolaria, and sometimes are mainly composed of closely compacted masses of such siliceous shells; of this kind are many quartzites of the Jura (§ 243). These Jurassic quartzes (Switzerland), as well as the Tertiary marls (Barbados) and clays (Nicobar Islands), are to be regarded as "fossil Radiolarian ooze" (§ 237). Dense masses of compressed Spumellaria and Nassellaria form the principal part of these rocks. Isolated or in smaller quantities, fossil Polycystina, belonging to different families of Spumellaria and Nassellaria, also occur in in other rocks, and even in some of PalÆozoic origin. Since specimens have also been recently found both in Silurian and Cambrian strata, it may be stated that as regards their historical distribution, Radiolaria occur in all fossiliferous sedimentary deposits, from the oldest to those of the present time.

242. Cainozoic Radiolaria.—The great majority of fossil Radiolaria which have hitherto been described, belong to the Cainozoic or Tertiary period, and in fact, to its middle portion, the Miocene period. At this period the richest and most important of all the Radiolarian formations were deposited, such as the pure "Polycystine marl" of Barbados (see note A), also that of Grotte in Sicily (see note B), and the clay of the Nicobar Islands (see note C). Besides the above-mentioned deposits, which may be designated "pure" fossil Radiolarian ooze, many deposits containing these organisms have recently been discovered in widely separated parts of the earth, partly of the nature of tripoli or marl, partly resembling clay. Among these may be mentioned in the first place many coasts and islands of the Mediterranean, both on the south coast of Europe (Sicily, Calabria, Greece), and the north coast of Africa (from Oran to Tripoli). The extensive layers of tripoli which are found in these Mediterranean Tertiary mountains belong to the upper Miocene (Tortona stage), and consist partly of marl rich in calcareous matter, and resembling chalk, partly passing over into plastic clay or "Kieselguhr" (§ 246). The quantity of Radiolaria contained varies, and is more conspicuous the fewer the calcareous shells of Foraminifera present. Similar Tertiary Polycystine formations occur in some parts of America (see note D); probably they have a very wide distribution. In their general morphological characters, the Tertiary Spumellaria and Nassellaria are related to those forms which are found in the recent Radiolarian ooze of the depths of the Pacific, especially to the species which are characteristic of the Challenger Stations 225, 226, 265 and 268. Many living genera and families (e.g., most Larcoidea and Stephoidea) have not yet been found in the Tertiary formations.

A. The famous Polycystine marl of Barbados in the Antilles, which Robert Schomburgk discovered forty years ago, belongs to the Miocene formation, and is the richest and best known of all the important Radiolarian deposits (see L. N. 16, pp. 5-8). After Ehrenberg had published in December 1846 the first preliminary communication regarding its composition out of masses of well-preserved Polycystina, he was able in the following year to describe no less than 282 species from it; he distributed these in 44 genera and 7 families (L. N. 4, 1847, p. 54). In the year 1854 Ehrenberg published figures of 33 species in his Mikrogeologie (L. N. 6, Taf. xxxvi.); but it was only in 1873 that he published descriptions of 265 species (Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, Jan. 30, pp. 213-263). Finally there followed in 1875 his Fortsetzung der Mikrogeologischen Studien, mit specieller RÜcksicht auf den Polycystinen-Mergel von Barbados (L. N. 25). On the thirty plates which accompany this the last work of Ehrenberg, 282 species are figured and named, of which 54 are Spumellaria (13 SphÆroidea, 8 Prunoidea, 33 Discoidea), and 228 Nassellaria (2 Stephoidea, 38 Spyroidea, and 188 Cyrtoidea). The fourth section of this memoir contains a survey of the Polycystine formation of Barbados (pp. 106-115), and the fifth section the special description of a large specimen of rock from Mount Hillaby in Barbados (see also L. N. 28, p. 117, and L. N. 41, pp. 476-478). The account given by Ehrenberg of the Polycystina of Barbados is in many respects very incomplete, and very far from exhausting this rich mine of remarkable forms. This may be readily seen from the twenty-five plates of figures of Polycystins in the Barbados Chalk Deposit published by Bury in 1862 (L. N. 17). The number of species here figured (140 to 142) is about half of those given by Ehrenberg; and there are among them numerous generic types, some of great interest, which were entirely overlooked by the latter; e.g. Saturnalis (SphÆroidea), Cannartidium (Prunoidea), Tympanidium (Stephoidea), Cinclopyramis (Cyrtoidea), &c. Finally, Ehrenberg always (until 1875) ignored Bury's atlas, which had been published thirteen years ago and was quite accessible to him. How different were the contents of the two works may easily be seen from the following abstract.

Comparative View of the Species of Fossil Radiolaria from Barbados made known by the figures of Bury in 1862 and of Ehrenberg in 1875.

Legion. Order. Bury. Ehrenberg. Total.
II. Legion
Spumellaria
(Peripylea).		 brace 1. SphÆroidea 16 13 29
2. Prunoidea 10 8 18
3. Discoidea 37 33 70
 
II. Legion
Nassellaria
(Monopylea).		 brace 4. Stephoidea 5 2 7
5. Spyroidea 13 38 51
6. Cyrtoidea 60 188 248
Total, 141 282 423
Legion. Order. Bury. Ehrenberg. Total.
II. Legion
Spumellaria
(Peripylea).		 1. SphÆroidea 16 13 29
2. Prunoidea 10 8 18
3. Discoidea 37 33 70
II. Legion
Nassellaria
(Monopylea).		 4. Stephoidea 5 2 7
5. Spyroidea 13 38 51
6. Cyrtoidea 60 188 248
Total, 141 282 423

B. The Cainozoic Polycystine tripoli or marl of the Mediterranean coast, which is probably always of Miocene origin, forms very extensive mountain ranges both in the south of Europe (Sicily, Calabria, Greece) and in the north of Africa (from Oran to Tripoli) (§ 246). Hitherto, however, only one locality has been thoroughly investigated, namely, Grotte in the province of Girgenti in Sicily (L. N. 35). In the accurate account which was given of it by StÖhr in 1880, 118 species were described, distributed in 40 genera (L. N. 35; pp. 72-84); of these 118 species 78 are quite new, 25 are identical with previously known fossils, and 29 identical with living forms. Among them are 73 Spumellaria (28 SphÆroidea, 8 Prunoidea, and 37 Discoidea), but only 40 Nassellaria (1 Stephoidea, 6 Spyroidea, and 33 Cyrtoidea), and 5 PhÆodaria (Dictyochida). The other parts of Sicily from which the same upper Miocene tripoli has been investigated (belonging to the Tortona stage) have proved less rich than Grotte. The best known of these places is Caltanisetta, since upon three genera discovered here (Haliomma, Cornutella, Lithocampe) the group Polycystina was founded by Ehrenberg in 1838 (see L. N. 16, p. 3). Afterwards 31 species were described from this locality, of which 23 were again found in Grotte. The richest deposit on the Mediterranean coast, however, appears to be at Oran. A small specimen of the Kieselguhr found there, which was recently sent to me by Professor Steinman, proved to be pure Radiolarian ooze, very similar to that now found in the Central Pacific, and contained many hitherto undescribed species; it is deserving of careful investigation and comparison.

C. Regarding the Tertiary Radiolarian clay of the Nicobar Islands, see § 247 and L. N. 25, pp. 116-120. Its fauna is incompletely known; probably it is of Miocene or Oligocene origin.

D. Cainozoic tripoli, containing larger or smaller quantities of Radiolaria, appears to be rather widely distributed in America. Ehrenberg has described such from South America (polishing-slate from Morro di Mijellones, on the coast between Chili and Bolivia), and from North America (Richmond and Petersburg in Virginia, Piscataway in Maryland). Similar deposits are also found in the Bermuda Islands (L. N. 4, 1855-56; L. N. 6, Taf. 18; L. N. 16, pp. 3-9; L. N. 41, pp. 475-478, and L. N. 25, pp. 2-6).

243. Mesozoic Radiolaria.—From the Mesozoic or Secondary period numerous well-preserved Radiolaria have recently been described. They belong for the most part to the Jurassic formation (see notes A, B, C), whilst the more recent Chalk (see note D) and the older Trias (see note E) have hitherto yielded but few species. All the main divisions of the Jura, both the upper (Malm) and the middle (Dogger), and especially the lower (Lias) appear in certain localities to be very rich in well-preserved shells of fossil Polycystina. Most of these are aggregated together in coprolites and quartzites (jasper, chert, flint, &c., § 248). The majority are Cyrtoidea, the minority SphÆroidea and Discoidea in almost equal proportions; a few Beloidea (SphÆrozoum) and PhÆocystina (Dictyocha) are also found among them. The general morphological character of these Jurassic Radiolaria is very different from that of the nearly related Tertiary and living forms. In general, their siliceous shells are firmer and more massive, usually also somewhat larger, but of simpler structure. The manifold delicate appendages (spines, bristles, feet, wings, &c.) which are so richly developed in the living Spumellaria and Nassellaria, and are also well shown in the Tertiary species, are entirely wanting in the majority of the Jurassic Polycystina. The SphÆroidea and Prunoidea are all simple spherical or ellipsoidal lattice-shells (MonosphÆrida); concentric lattice-shells (PolysphÆrida) are entirely wanting. The Cyrtoidea are, for the most part, devoid of radial processes or basal feet (Eradiata); triradiate and multiradiate forms, such as are found abundantly in the recent and Tertiary formations, are very rare. The large number of many-jointed forms (Stichocyrtida) and of Cyrtoidea with latticed basal opening is very striking.

A. The most important work on the Jurassic Radiolaria, regarding which but little was known prior to the year 1885, is the valuable and in some respects very interesting BeitrÄge zur Kenntniss der fossilen Radiolarien aus Gesteinen des Jura, by Dr. RÜst of Freiburg i. B. (1885, PalÆontographica, Bd. xxxi. 51 pp. with 12 plates). Unfortunately this important work was issued only when about half of the present Report was printed off, so that it was no longer possible to include the 234 species there described in its systematic part. I have therefore elsewhere given a list of the Jurassic Radiolaria, and at present only make the following remarks:—Of the 234 species described, the larger half (130) belong to the Nassellaria (Cyrtoidea), the smaller half (102) to the Spumellaria (38 SphÆroidea, 14 Prunoidea, and 50 Discoidea). In addition, there are 2 PhÆodaria depicted, and several spicules which are probably to be referred to the Beloidea. Among the 130 Cyrtoidea (of which 2 are described as Botryodea), there are 24 Monocyrtida, 14 Dicyrtida, 22 Tricyrtida, and 70 Stichocyrtida. Just as striking as the predominant number of the last is the fact that there are only very few triradiate (9) and multiradiate (4) species found among these 130 Cyrtoidea, as also the large number of species with latticed basal opening; Stephoidea appear to be entirely wanting. The rich material of jasper, chert, flint, and coprolites in which Dr. RÜst found these Radiolaria, is derived for the most part from the Jurassic rocks of Germany (Hanover, South Bavaria), Tyrol, and Switzerland (compare § 248).

C. From the Lias of the Alps and more particularly "from the lower Liassic beds of the Schafberg near Salzburg," Dr. Emil von Dunikowski in 1882 described 18 species of fossil Radiolaria (L. N. 44, pp. 22-34, Taf. iv.-vi.); most of these are SphÆroidea and Discoidea and appear to have been more or less altered by petrological changes; their spongy structure is probably secondary.

D. Cretaceous Radiolaria have been hitherto described only in very small numbers; quite recently Dr. RÜst has found a larger number chiefly in flints from the English chalk, but they have not yet been published. In 1876 Zittel described 6 very well-preserved species from the upper chalk of North Germany (L. N. 29, pp. 76-96, Taf. ii.); among them were 1 SphÆroidea, 1 Discoidea, 1 Dictyocha, and 3 Cyrtoidea.

E. Triassic Radiolaria have recently been discovered by Dr. RÜst in chert, but have not yet been described.

244. PalÆozoic Radiolaria.—The number of Radiolaria which are known from the PalÆozoic or Primary formations is much less than from either the Mesozoic or Cainozoic periods. Here, however, the investigations of recent times have yielded important information; a few species, at all events, of Polycystina (mostly SphÆroidea) are now known from various PalÆozoic formations, and not only from the Permian ("Zechstein") and the Coal-measures, but also from the older Devonian and Silurian systems. Even in the still older Cambrian rocks a few fossil Radiolaria have been found. All these PalÆozoic Radiolaria are Polycystina of very simple form and primitive structure, mostly simple Spumellaria (latticed spheres, ellipsoids, lenses, &c.), but partly also simple Nassellaria.

The important discoveries which have recently been made by Dr. RÜst regarding the occurrence of Radiolaria in all the PalÆozoic formations have not yet been published. From conversations with this estimable palÆontologist I have learned, however, that he has pursued his fruitful investigation of the Mesozoic quartzites (§ 243), and has met with no less success in the case of similar PalÆozoic structures. Although the number of species hitherto discovered is relatively small, the important conclusion appears to be warranted that they extend as far as the Silurian and Cambrian systems. All these very ancient Spumellaria (SphÆroidea) and Nassellaria (Cyrtoidea) exhibit very primitive structural relations. The occurrence of fossil Polycystina in the Carboniferous formation of England has been incidentally mentioned by W. J. Sollas:—"In the carboniferous beds of North Wales pseudomorphs of Radiolaria in calcite occur, along with minute quartz crystals" (Ann. and Mag. Nat. Hist., 1880, ser. 5, vol. vi. p. 439); and in the siliceous slate-beds of Saxony Rothpletz has shown the existence of a few SphÆroidea (Zeitschr. d. Deutsch. Geol. Gesellsch., 1800, p. 447).

245. Abundance of Radiolaria in the Various Rocks.—The relative quantity of well-preserved or at all events recognisable Radiolaria in the different rocks is very variable. In this respect three different degrees may be distinguished, which may be called shortly "pure, mixed, and poor" Radiolarian formations. The pure Radiolarian rocks consist for the greater part (usually much more than half, sometimes even more than three-quarters) of closely compacted often calcined masses of siliceous Polycystine shells. To this category belong the pure Miocene Polycystine marls of Barbados (§ 246), the Tertiary Polycystine clay of the Nicobar Islands (§ 247), and the Polycystine quartz of the Jura (§ 248). All these pure Radiolarian rocks may be regarded as fossil Radiolarian ooze (§ 237), and are certainly of deep-sea origin, having probably been deposited at depths greater than 2000 fathoms. Their palÆontological character also is in favour of this view, for the abyssal Osculosa (§ 235) are more abundant and richer in species than the pelagic Porulosa (§ 233). The elevation of this deep-sea layer above the surface of the sea appears to have taken place but seldom; it has only been observed on a large scale at Barbados and in the Nicobar Islands. The mixed Radiolarian rocks are much more common; they were probably deposited at much less depths, or perhaps are not true deep-sea formations at all. The siliceous shells of Polycystina always constitute less than half (sometimes less than one-tenth) of their mass, and are less prominent than other siliceous remains (Diatoms), or calcareous remains (Foraminifera), or in some cases than the mineral constituents (pumice, &c.). To this group belong many of the above-mentioned Tertiary marls and clays (especially the Mediterranean Tripoli), also many flints, cherts, and other quartzites from Mesozoic strata (especially from the Jura), and probably also some palÆozoic quartzites. The marine ooze from which they have originated may have been deposited at very various, even at slight, depths of the ocean. Formations poor in Radiolaria, which contain only a few species of Spumellaria and Nassellaria mingled with other fossil remains and mineral particles, occur in all formations and are probably very widely distributed. Further careful examination of thin sections (especially of coprolites) will yield here a rich harvest of new forms. Both the mixed and the pure Radiolarian formations may be divided according to their petrographic characters into three groups, which, however, are connected by intermediate varieties—(1) soft, chalky marl (§ 246), (2) plastic clay (§ 247), and (3) hard, flinty quartz (§ 248).

246. Radiolarian Marl.—Those soft, friable rocks, which contain a large quantity of calcareous matter, but consist for the most part of the shells of Spumellaria and Nassellaria, are called Radiolarian or Polycystine marl, often more correctly Polycystine tripoli; the best known example of them is the chalky marl of Barbados in the Antilles (§ 242). The Tertiary mountain system of this island, which in Mount Hillaby rises to a height of 1147 feet and includes about 15,800 acres, consists almost exclusively of these remarkable masses of rock. Most of it appears as a soft, earthy, often chalky marl, with a considerable but variable amount of calcareous matter. Those specimens, the greater half of which is composed of well-preserved siliceous shells of Polycystina, and which contain little lime, approach the tripoli and "Kieselguhr." Those specimens, however, which contain the largest amount of calcareous matter resemble common writing chalk in consistency, and consist for the most part of shells of Foraminifera and their fragments; of these there are only few species but large numbers of individuals, generally in small fragments with a fine calcareous powder between them. They may be regarded as fossil Globigerina ooze (§ 238). In a third group of specimens from Barbados the quantity of fragments of pumice and other volcanic matters predominates; the amount of clay is also very considerable; these deposits pass over partly into actual clay partly into volcanic tuff. A fourth group exhibits relations to a coarser often ferruginous material, and although the shells of Polycystina are less abundant in it, still it may be shown to be composed largely of fragments and metamorphosed remains of them. The colour of this deposit, which in some places passes over into sandstone, in others into clay, is usually rather dark, grey, brown, sometimes red and occasionally black (bituminous). The Radiolarian marls of the first two groups, which sometimes approach the white chalk, sometimes the Kieselguhr, are grey, or even pure white (see note A). The same constitution is exhibited by the yellowish or white, very light and friable Polycystine marls of Sicily, which in Caltanisetta approach the chalk, and in Grotte the Kieselguhr. In Greece (Ægina, Zante, &c.), on the other hand, they pass over into plastic clay, and the same occurs in the Baden marl of the Vienna basin. In North Africa, however, on the Mediterranean shores of which the Radiolarian marl seems to be very widely distributed (from Tripoli to Oran), it sometimes becomes changed into actual firm polishing slate, sometimes into pulverulent Kieselguhr or tripoli (Terra tripolitana, see note B). Most of these Radiolarian marls appear to date from the middle Tertiary (Miocene) period, and to be deep-sea formations.

A. The Polycystine marl of Barbados appears at different parts of the island to present greater variations in its petrographical and zoographical composition than would appear from Ehrenberg's description (1875, L. N. 25, pp. 106-116). Through the kindness of one of my former students, Dr. Dorner, to whom I take this opportunity of expressing my thanks for the favour, I received a large number of specimens of Barbados rock, taken from various parts of the island, and they exhibit very great variations in their external appearance, their chemical composition, and the Radiolaria which they contain. The white specimens resembling Kieselguhr contained approximately 60 to 70 per cent. by volume of Radiolarian shells, the yellowish marl 40 to 50 per cent., and the brown and black (bituminous) marl 10 to 20 per cent. or less. Two analyses of the first, which my friend Dr. W. Weber was good enough to carry out, yielded different results from those which are given by Ehrenberg on the basis of Rammelsberg's analyses (L. N. 25, p. 116). The results of both are here given for comparison.

Ehrenberg-Rammelsberg
(Fragment from Hillaby).		 Weber I.
(Chalk-like Fragment).		 Weber II.
(Tripoli-like Fragment).
Silicate of alumina, 59.47 Silica, 52.2 71.3
Alumina and oxide of iron, 1.95 Alumina (with traces of oxide of iron), 12.3 11.2
Calcium carbonate, 34.31
Water, 3.67 Lime and magnesia, 31.9 14.8
Carbon dioxide, 3.2 02.7
—— —— ——0
Total, 99.40 Total, 99.6 100.00

For further comparison I here add the three different analyses of Miocene Tripoli-marls from Sicily, given by StÖhr on the authority of Fremy, Schwager, and Mottura (Tagebl. d. fÜnfzigsten Versamml. Deutsch. Naturf. u. Aertzte in MÜnchen, 1877, p. 163).

Composition. Tripoli from
Licata
(Fremy).		 Tripoli from
Grotte
(Schwager).		 Tripoli from
Caltanisetta
(Mottura).
Silica, 30.98 58.58 68.6
Alumina, 17.54 11.51 brace 3.6
Oxide of iron, 0.33 1.84
Lime, brace 38.09 brace 8.49 brace 12.1
Magnesia, 0.41
Water and organic matter, brace 13.06 brace 11.26 brace 15.2
Carbonic acid, 7.12
100.00 99.21 99.5

B. The Radiolarian marl of the Mediterranean appears, judging by the accounts already published, to stretch along a considerable part of the coast in the earlier and middle Tertiary formations; thus it occurs of similar composition in widely separated localities, in Sicily, Calabria, Zante, and Greece; in North Africa from Tripoli to Oran and probably much farther. So long ago as 1854 Ehrenberg, in his Mikrogeologie (L. N. 6) gave a series of important, even if incomplete, communications regarding the "chalky white calcareous marl of Caltanisetta" (Taf. xxii.), the "Platten marl of Zante" (Taf. xx.), the "plastic clay of Ægina" (Taf xix.), and the "polishing slate of Oran" (Taf. xxi.). In 1880 StÖhr showed in his fundamental description of the Tripoli from Grotte in Sicily (L. N. 35) that its Radiolarian fauna is much richer than Ehrenberg supposed. The same is the case in the Tripoli of Caltanisetta, and also in the Baden marl of the Vienna basin. The richest deposit appears to be the pure Kieselguhr-like Tripoli from Oran; a small specimen, which was recently sent to me by Professor Steinmann of Freiburg, i. B., contained many hitherto undescribed species, and was at least as rich as the purest Barbados marl.

247. Radiolarian Clays.—Among the Radiolarian or Polycystine clays we include the firm, often plastic, formations, which contain a larger proportion of Radiolaria than of other organic remains. The first of these to be mentioned is the Cainozoic formation of the Nicobar Islands in Further India, which rises to a height of 2000 feet above the level of the sea, and consists for the most part of coloured masses of clay of varying constitution; on Car Nicobar these are mostly grey or reddish, on the Island of Camorta they are partly strongly ferruginous and red and yellow (e.g. at Frederickshaven), partly white and light, like meerschaum (e.g. at Mongkata). The latter varieties appear to pass over into pure loose Polycystine marl like that of Barbados, the former into calcareous sandstone. Although the Polycystine clays of the Nicobar Islands are as yet only very incompletely known, it may be concluded with great probability that they are true deep-sea formations and nearly allied to those recent forms of red clay, which by their abundance in Radiolaria most nearly approach the Radiolarian ooze, such for example as the red clay of the North Pacific between Japan and the Sandwich Islands (Stations 241 to 245, compare §§ 229 and 239). With this view agrees also the greater or less quantity of pumice dust and other volcanic products. Probably Radiolarian clays like those of the Nicobar Islands occur also in other Tertiary rocks; part of the Barbados marl passes by gradually increasing content of clay into such; and in this case also the amount of included pumice is often considerable. Many mixed Radiolarian marls of the Mediterranean (e.g., of Greece and Oran) also appear to pass over at certain points into Radiolarian clay.

The Radiolarian clays of the Nicobar Islands are unfortunately very incompletely known both as regards their geological nature and their palÆontological composition. The communications of Rink (Die Nikobaren-Inseln, eine geographische Skizze, Kopenhagen, 1847) and of Ehrenberg (L. N. 6, p. 160 and L. N. 25, pp. 116 to 120) leave many important questions unanswered. The latter has only figured twenty-three species in his Mikrogeologie (L. N. 6, Taf. xxxvi.). In his tabular list of names (L. N. 25, p. 120) he only incompletely records thirty-nine species, although in 1850, immediately after the first examination of the Nicobar clay, he had distinguished "more than a hundred species, partly new, partly identical with those of Barbados" (L. N. 16, p. 8). I have unfortunately been unable in spite of many efforts, to obtain for investigation a specimen of Nicobar clay. The only microscopical preparation (from Ehrenberg's collection), which I was able to examine, contained several hitherto undescribed species. A thorough systematic examination of these important Radiolarian clays is a pressing necessity, especially as they seem to be markedly different from those of the Mediterranean (from Ægina, Zante, &c.).

248. Radiolarian Quartzes.—Under the name Radiolarian or Polycystine quartzes are included those hard, siliceous rocks, which consist for the most part of the closely compacted shells of Spumellaria and Nassellaria. To these "cryptocrystalline quartzes," or better, quartzites, belong more especially the pure Radiolarian formations of the Jura, which have been described as flint, chert, jasper, as well as other cryptocrystalline quartzites. Most of the rocks of this nature hitherto examined are from Germany (Hanover, South Bavaria), Hungary, Tyrol, and Switzerland; others are known from Italy (Tuscany). They occur both in the upper and middle, but especially in the lower Jurassic formation (also in the lower layers of the Alpine Lias). A small part of them has been examined in their primary situation (the red jaspers of AllgÄu and Tyrol), the greater part, however, only as loose rolled stones in secondary situations (thus in Switzerland in the breccia of the Rigi, in the conglomerate of the Uetli-Berg, and in many boulders of the Rhine, the Limmat, the Reuss, and the Aar). The greatest abundance, however, of Jurassic Radiolaria has been yielded by the silicified coprolites from the Lias of Hanover. These "Radiolarian coprolites" are roundish or cylindrical bodies, which may attain the size of a goose-egg; they probably originated from Fish or Cephalopods, which had fed upon Crustacea, Pteropoda, and similar pelagic organisms, whose stomachs were already full of Radiolarian skeletons. Next to the coprolites the richest is the red jasper, whose colour varies from bright to dark red; it constitutes a true "silicified deep-sea Radiolarian ooze." The "Aptychus beds" also of South Bavaria and Tyrol are very rich, and have furnished about one-third of all the Radiolaria known from the Jura; most of the species too are very well preserved (compare § 243).

Regarding the remarkable composition and manifold varieties of the Jurassic Radiolarian quartz, the very full treatise of Dr. RÜst may be consulted (L. N. 51). The very interesting Radiolarian coprolites, which that author has discovered in the lower and middle Jura of Hanover, occur in astonishing numbers in the iron mines at the village of Gross-Ilsede, four and a half miles south of the town of Peine. They constitute from 2 to 5 per cent. by weight of the Liassic iron ore; of this latter, in the year 1883 alone, not less than two hundred and eighty million kilograms were excavated. It is very probable that the careful microscopic examination of thin sections of coprolites, as well as of flints, chert, jasper, and other quartzites, would yield a rich harvest of fossil Radiolaria in other formations also. In Italy Dante Pantanelli has discovered interesting Polycystine jaspers in Tuscany (L. N. 36, 45); these also appear to occur in the Jura (compare § 243, and L. N. 51, pp. 3-10).

249. Fossil Groups.—The preservation of Radiolaria in the fossil state is, of course, primarily dependent on the composition of their skeleton. Hence the Acantharia, whose acanthin skeleton although firm is readily soluble, are never found fossil. The same is true of the skeletons of the PhÆodaria, which consist of a silicate of carbon; here, however, a single exception is found in the Dictyochida, a subfamily of the Cannorrhaphida, the isolated parts of whose skeletons appear to consist of pure silica, and are often found fossil. Of the two other legions those families which possess no skeleton are of course excluded; the Nassellida among the Nassellaria, and the Thalassicollida and Collozoida among the Spumellaria. Thus of the 85 known families there remain scarcely 55 of which the skeletons may be expected in the fossil state; and of these scarcely half have been actually observed in this condition. Of the 20 orders of this class enumerated in § 155, the following 9 may be, for palÆontological and geological purposes, completely excluded:—(A) The 4 orders of Acantharia (1, Actinelida; 2, Acanthonida; 3, SphÆrophracta; 4, Prunophracta); (B) 3 orders of PhÆodaria (5, PhÆosphÆria; 6, PhÆogromia; 7, PhÆoconchia); (C) 1 order of Nassellaria (8, Nassoidea); (D) 1 order of Spumellaria (9, Colloidea). From a geological point of view the following 6 orders, although occasionally found fossil, are of quite subordinate importance:—(A) Among the Spumellaria (10, Beloidea, and 11, Larcoidea); (B) among the Nassellaria (12, Plectoidea; 13, Stephoidea; 14, Botryodea); (C) among the PhÆodaria (15, the PhÆocystina). On the other hand the following 5 orders, which are the main constituents of Radiolarian rocks, are of pre-eminent geological importance:—(A) Among the Spumellaria (16, SphÆroidea; 17, Prunoidea; 18, Discoidea); (B) among the Nassellaria (19, Spyroidea, and 20, Cyrtoidea). The numerical relation in which the different families of these orders appear in the Radiolarian formations may be seen on consulting § 157.

250. Fossil and Recent Species.—The fact that there are many Radiolaria living at the present day, whose shells are found fossil in Tertiary rocks, is of great phylogenetic and geological significance. This appeared to be the case even from the older observations upon the Polycystina of the Barbados marl (see note A), but more recent and extensive observations both upon these and upon the Miocene Radiolaria of Sicily, have shown that the number of these "living fossil" forms is much greater than was previously supposed (see note B). Among the Miocene Radiolaria numerous species, both of Spumellaria (especially SphÆroidea and Discoidea) and of Nassellaria (especially Spyroidea and Cyrtoidea) are not to be distinguished from the corresponding still living forms (see notes C, D). On the other hand, those genera, which are rich both in species and individuals (recent as well as fossil), present continuous series of forms which lead gradually and uninterruptedly from old Tertiary species to others still living, which are specifically indistinguishable from them. These interesting morphological facts are capable of direct phylogenetic application, and furnish valuable proofs of the truth of the theory of descent.

A. Ehrenberg, in his list of fossil Polycystina (L. N. 25, pp. 64-85, 1875), records 325 species of which 26 are still living.

B. StÖhr, in his list of Miocene Radiolaria from Grotte (L. N. 35, p. 84, 1880), records 118 species, of which 29 are still living.

D. From the comparative investigations, which I have made during the last ten years into the recent deep-sea Radiolaria of the Challenger collection and the Miocene Polycystina of Barbados, it appears that about a quarter of the latter are identical with living species of the former.

BIBLIOGRAPHICAL SECTION.

CHAPTER XI.—LITERATURE AND HISTORY.

251. List of Publications from 1834 to 1884:—

Note.—In the text the references to the following publications are indicated by the letters L. N.

1. 1834. Meyen, F., Palmellaria (Physematium, SphÆrozoum), in BeitrÄge zur Zoologie, gesammelt auf einer Reise um die Erde. Nova Acta Acad. CÆs. Leop.-Carol., vol. xvi., Suppl., p. 160, Taf. xxviii. figs. 1-7.

2. 1838. Ehrenberg, G., Polycystina (Lithocampe, Cornutella, Haliomma) in Ueber die Bildung der Kreidefelsen und des Kreidemergels durch unsichtbare Organismen. Abhandl. d. k. Akad. d. Wiss. Berlin, p. 117.

3. 1839. Ehrenberg, G., Ueber noch jetzt lebende Thierarten der Kreidebildung (Haliomma radians). Abhandl. d. k. Akad. d. Wiss. Berlin, p. 154.

4. 1844-1873. Ehrenberg, G., VorlÄufige Mittheilungen Über Beobachtungen von Polycystinen. Monatsber. d. k. preuss. Akad. d. Wiss. Berlin. Republished with illustrations in the Mikrogeologie (L. N. 6) and in the two treatises of 1872 (L. N. 24) and 1875 (L. N. 25). Compare the Monatsberichte of 1844 (pp. 57, 182, 257), of 1846 (p. 382), of 1847 (p. 40), of 1850 (p. 476), of 1854 (pp. 54, 205, 236), of 1855 (pp. 292, 305), of 1856 (pp. 197, 425), of 1857 (pp. 142, 538), of 1858 (pp. 12, 30), of 1859 (p. 569), of 1860 (pp. 765, 819), of 1861 (p. 222), of 1869 (p. 253), of 1872 (pp. 300-321), of 1873 (pp. 214-263). Only one of these small papers is of permanent value, The First Systematic Arrangement of the Polycystina in 7 families, 44 genera, and 282 species (Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, 1847, p. 54). Compare my Monograph (1862, L. N. 16), pp. 3-12, 214-219.

5. 1851. Huxley, Th., Upon Thalassicolla, a new Zoophyte. Ann. and Mag. Nat. Hist., ser. 2, vol. viii. pp. 433-442, pl. xvi.

6. 1854. Ehrenberg, G., Mikrogeologie. Figures of numerous Polycystina on 8 plates; Taf. xviii. figs. 110, 111; Taf. xix. figs. 48-56, 60-62; Taf. xx. Nr. i., figs. 20-25, 42; Taf. xxi. figs. 51-56; Taf. xxii. figs. 20-40; Taf. xxxv. A., Nr. xix. A. fig. 5; Taf. xxxv. B. figs. 16-23; Taf. xxxvi. figs. 1-33.

7. 1855. Bailey, J. W., Notice of Microscopic Forms of the Sea of Kamtschatka. Amer. Journ. Sci. and Arts, vol. xxii. p. 1, pl. i.

8. 1855. MÜller, Johannes, Ueber SphÆrozoum und Thalassicolla. Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 229.

9. 1855. MÜller, Johannes, Ueber die im Hafen von Messina beobachteten Polycystinen (Haliomma, Eucyrtidium, Dictyospyris, Podocyrtis). Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 671.

10. 1856. MÜller, Johannes, Ueber die Thalassicollen, Polycystinen und Acanthometren des Mittelmeeres. Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 474.

11. 1858. MÜller, Johannes, ErlÄuterung einiger bei St. Tropez am Mittelmeer beobachteter Polycystinen und Acanthometren. Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 154.

12. 1858. MÜller, Johannes, Ueber die Thalassicollen, Polycystinen und Acanthometren des Mittelmeeres, Abhandl. d. k. Akad. d. Wiss. Berlin, pp. 1-62, Taf. i.-xi. (The fundamental treatise on the Radiolaria.)

13. 1858. Schneider, Anton, Ueber zwei neue Thalassicollen von Messina. Archiv f. Anat. u. Physiol., p. 38, Taf. iii. B, figs. 1-4.

14. 1858. ClaparÈde et Lachmann, Echinocystida (Plagiacantha et Acanthometra). Études sur les Infusoires et les Rhizopodes, p. 458, pl. xxii. figs. 8, 9; pl. xxiii. figs. 1-6.

15. 1860. Haeckel, Ernst, Ueber neue lebende Radiolarien des Mittelmeeres. Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, pp. 794, 835.

16. 1862. Haeckel, Ernst, Die Radiolarien (Rhizopoda radiaria). Eine Monographie. 572 pp. fol. with an Atlas of 35 Copperplates.

17. 1862. Bury, Mrs., Polycystins, figures of remarkable forms in the Barbados Chalk Deposit. Ed. ii. By M. C. Cooke, 1868. 25 quarto plates, photographed from drawings by hand, containing many forms overlooked by Ehrenberg from Barbados.

18. 1863 Harting, Paul, Bijdrage tot de Kennis der mikroskopische Fauna en Flora van de Banda-Zee (Diep-Zee-Polycystinen). Verhandl. d. Kon. Akad. van. Wetensch. Amsterdam, vol. ix. p. 30, pls. i.-iii.

19. 1865. Haeckel, Ernst, Ueber den Sarcode-KÖrper der Rhizopoden (Actinelius, Acanthodesmia, CyrtidosphÆra, &c.). Zeitschr. f. wiss. Zool., Bd. xv. p. 342, Taf. xxvi.

20. 1867. Schneider, Anton, Zur Kenntniss des Baues der Radiolarien (Thalassicolla). Archiv f. Anat. u. Physiol., 1867, p. 509.

21. 1870. Haeckel, Ernst, BeitrÄge zur Plastiden Theorie (Myxobrachia; Amylum in den gelben Zellen). Jenaische Zeitschr. fÜr Naturw., Bd. v. p. 519-540, Taf. xviii.

22. 1871. Cienkowski, L., Ueber SchwÄrmer-Bildung bei Radiolarien. Archiv f. mikrosk. Anat., Bd. vii. p. 372-381, Taf. xxix.

23. 1872. Wagner, N., Myxobrachia Cienkowskii. Bull. d. Acad. St. Petersburg, vol. xvii. p. 140.

24. 1872. Ehrenberg, Gottfried, Mikrogeologische Studien Über das kleinste Leben der Meeres-TiefgrÜnde aller Zonen und dessen geologischen Einfluss. Abhandl. d. k. Akad. d. Wiss. Berlin, 1872. Mit 12 Tafeln. (The Latin diagnoses of 113 new species here mentioned are given in the Monatsberichte of April 25, 1872, pp. 300-321.)

25. 1875. Ehrenberg, Gottfried, Polycystinen-Mergel von Barbados (Fortsetzung der Mikrogeologischen Studien). Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, 168 pag. mit 30 Tafeln. (The Latin diagnoses of 265 species here recorded are given in Namensverzeichniss der fossilen Polycystinen von Barbados. Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, Jan. 30, 1873, pp. 213-263.)

26. 1876. Hertwig, Richard, Zur Histologie der Radiolarien. Untersuchungen Über den Bau und die Entwickelung der SphÆrozoiden und Thalassicolliden. 91 pp. with 5 plates.

27. 1876. Murray, John, Challengerida. Preliminary Reports on Work done on board the Challenger. Proc. Roy. Soc. Lond., vol. xxiv. pp. 471-536, pl. xxiv.

28. 1876. Zittel, Karl, PalÆozoologie, Bd. i. pp. 114-126, figs. 46-56.

29. 1876. Zittel, Karl, Ueber fossile Radiolarien der oberen Kreide. Zeitschr. d. deutsch. geol. Gesellsch., Bd. xxviii. pp. 75-96, Taf. ii. (with figures of six Cretaceous species).

30. 1877. Mivart, St. George, Notes touching recent researches on the Radiolaria. Journ. Linn. Soc. Lond. (Zool.), vol. xiv. pp. 136-186. (Historical sketch of previous literature.)

31. 1877. Wyville Thomson, The Voyage of the Challenger—The Atlantic, vol. i. pp. 231-237, figs. 51-54; vol. ii. pp. 340-343, figs. 58, 59, &c.

32. 1878. Haeckel, Ernst, Das Protistenreich, eine populÄre Uebersicht Über das Formengebiet der niedersten Lebewesen, pp. 101-104.

33. 1879. Hertwig, Richard, Der Organismus der Radiolarien. Jenaische Denkschriften, Bd. ii. Taf. vi.-xvi. pp. 129-277.

34. 1879. Haeckel, Ernst, Ueber die PhÆodarien, eine neue Gruppe kieselschaliger mariner Rhizopoden. Sitzungsb. med.-nat. Gesellsch. Jena, December 12, 1879.

35. 1880. StÖhr, Emil, Die Radiolarien-Fauna der Tripoli von Grotte (Provinz Girgenti in Sicilien). PalÆontographica, Bd. xxvi. pp. 71-124, Taf. xvii.-xxiii. A preliminary communication regarding this fauna from the tripoli is given in Tagebl. d. Naturf. Versamml. MÜnchen, 1877.

36. 1880. Pantanelli, Dante, I Diaspri della Toscana e i loro fossili. Real. Accad. dei Lincei, ser. 3, vol. vii. pp. 13-34, Tab. i. Radiolaria di Calabria. Atti. Soc. Tosc., p. 59.

37. 1881. Haeckel, Ernst, Prodromus Systematis Radiolarium, Entwurf eines Radiolarien-Systems auf Grund von Studien der Challenger-Radiolarien. Jenaische Zeitschr. fÜr Naturw., Bd. xv. pp. 418-472.

38. 1881. Brandt, Karl, Untersuchungen an Radiolarien. Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, (April 21), pp. 388-404, Taf. i.

39. 1882. Brandt, Karl, Ueber die morphologische und physiologische Bedeutung des Chlorophylls bei Thieren. I. Artikel. Archiv f. Anat. u. Physiol., pp. 125-151, Taf. i. II. Artikel. Mittheil. a. d. Zool. Station zu Neapel, Bd. iv. pp. 193-302, Taf. xix., xx.

40. 1882. BÜtschli, Otto, BeitrÄge zur Kenntniss der Radiolarien-Skelette, insbesondere der der Cyrtida. Zeitschr. f. wiss. Zool., Bd. xxxvi. pp. 485-540, Taf. xxxi.-xxxiii.

41. 1882. BÜtschli, Otto, Radiolaria. In Bronn's Klassen und Ordnungen des Thierreichs. Bd. i., Protozoa, pp. 332-478, Taf. xvii.-xxxii.

42. 1882. Geddes, Patrick, Further Researches on Animals containing Chlorophyll. Nature, pp. 303-305.

43. 1882. Geddes, Patrick, On the Nature and Functions of the "Yellow Cells" of Radiolarians and Coelenterates. Proc. Roy. Soc. Edin., p. 377.

44. 1882. Dunikowski, Emil, Die Spongien, Radiolarien und Foraminiferen der Unter-Liassischen Schichten vom Schafberg bei Salzburg. Denkschr. d. k. Akad. d. Wiss. Wien, Bd. xlv. pp. 22-34. Taf. iv.-vi.

45. 1882. Pantanelli, Dante, Fauna miocenica di Radiolari del Appennino settentrional. Boll. Soc. Geol. Ital.

46. 1883. Haeckel, Ernst, Die Ordnungen der Radiolarien (Acantharia, Spumellaria, Nassellaria, PhÆodaria). Sitzungsb. med.-nat. Gesellsch. Jena, February 16, 1883.

47. 1883. Hertwig, Oscar, Die Symbiose oder das Genossenschaftsleben im Thierreich. 56. Versamml. Deutscher Naturf. u. Aerzte, Freiburg i/B.

48. 1883. RÜst, Wilhelm, Ueber das Vorkommen von Radiolarien-Resten in kryptokrystallinischen Quarzen aus dem Jura und in Koprolithen aus dem Lias. 56. Versamml. Deutscher Naturf. u. Aerzte, Freiburg i/B.

49. 1884. Car, Lazar, Acanthometra hemicompressa (= Zygacantha semicompressa). Zool. Anzeiger, p. 94.

50. 1884. Haeckel, Ernst, Ueber die Geometrie der Radiolarien (Promorphologie). Sitzungsb. med.-nat. Gesellsch. Jena, November 22, 1883.

251 A. Supplementary List of Works Published in 1885:—

51. 1885. D. RÜst, BeitrÄge zur Kenntniss der fossilen Radiolarien aus Gesteinen des Jura. 45 pp. 4to, and 20 plates. PalÆontographica, Bd. xxxi. (oder iii. Folge, vii. Band).

52. 1885. Karl Brandt, Die koloniebildenden Radiolarien (SphÆrozoeen) des Golfes von Neapel und der angrenzenden Meeres-Abschnitte. 276 pp. 4to, and 8 plates.

53. 1885. John Murray, Narrative of the Cruise of H.M.S. Challenger, with a general account of the scientific results of the Expedition. Vol i. First part, pp. 219-227, pl. A. Second part, pp. 915-926, pl. N. fig. 2.

54. 1885. Ernst Haeckel, System der Acantharien. Sitzungsb. med.-nat. Gesellsch. Jena, November 13.

Since the printing of this Report began in 1884 and was far advanced in 1885, it was impossible to include the important works of RÜst and Brandt (L. N. 51, 52) in the descriptive portion, so that they are only referred to in the Introduction.

251 B. Phaulographic Appendix:—

A list of absolutely worthless literature, which contains either only long known facts or false statements, and may hence be entirely neglected with advantage. Compare § 252, and also L. N. 26, p. 9.

55. 1865. Wallich, G. C., On the structure and affinities of Polycystina. Trans. Micr. Soc. Lond., vol. xiii. pp. 57-84. (Compare L. N. 26, p. 9.)

56. 1879. Wallich, G. C., Observations on the ThalassicollidÆ. Ann. and Mag. Nat. Hist., ser. 4, vol. iii. p. 97.

57. 1866. Stuart, Alexander, Ueber CoscinosphÆra ciliosa, eine neue Radiolarie (= Globigerina echinoides!!). Zeitschr. f. wiss. Zool., Bd. xvi. p. 328, Taf. xviii. (Compare L. N. 26, p. 9.)

58. 1870. Stuart, Alexander, Neapolitanische Studien. GÖttinger Nachr., p. 99, and Zeitschr. f. wiss. Zool., Bd. xxii. p. 290 ("Blue Siliceous Crystals" in Collozoum inerme!).

59. 1871. Macdonald, John Denis, Remarks on the Structure of Polycystina (Astromma Yelvertoni = Euchitonia MÜlleri). Ann. and Mag. Nat. Hist., ser. 4, vol. viii. p. 226.

60. 1871. Doenitz, W., Beobachtungen Über Radiolarien. Archiv f. Anat. u. Physiol., 1871, p. 71, Taf. ii. (Compare L. N. 26, p. 7.)

252. Progress of our Knowledge of the Radiolaria from 1862 to 1885.—The history of our scientific knowledge of the Radiolaria extends over about half a century (from 1834 to 1885). A historical and critical discussion of the works which appeared within the first twenty-eight years of this period (from 1834 to 1862) is contained in the historical introduction to my Monograph (L. N. 16, pp. 1-24); I shall therefore give here only a brief survey of the investigations published during the last twenty-three years (from 1862 to 1885). The most important steps in our progress during this period we owe to the following naturalists:—Cienkowski (1871), Ehrenberg (1872 and 1875), Richard Hertwig (1876 and 1879), Karl Brandt (1881 and 1885), BÜtschli (1882), and RÜst (1885). To the valuable works of these authors must be added a number of smaller contributions, which are recorded in the foregoing Bibliography. Some communications from dilettanti, written with insufficient knowledge of the subject, and hence of no value, are mentioned for the sake of completeness in the "Phaulographic Appendix" (compare L. N. 55-60, also L. N. 26, p. 9).

The first important advance in our knowledge of the organisation of the Radiolaria, made after the publication of my Monograph (1862), was the demonstration of the nature of the extracapsular "yellow cells." In the year 1870 I showed that these yellow cells contain starch (L. N. 21, p. 519). I regarded them, as did all authors up to that time, as integral parts of the Radiolarian organism, and hence considered this to be multicellular; for no doubt was possible regarding the true cellular nature of these remarkable, nucleated, yellow globules, which I had thoroughly studied in 1862. It was first shown by Cienkowski in 1871 that the yellow cells of the Collodaria remain unchanged even after the death of these organisms, "that they continue to grow uninterruptedly, and eventually multiply by division" (L. N. 22, pp. 378-380, Taf. xix. figs. 30-36). Cienkowski concluded from these important observations that the yellow cells are not integral parts of the Radiolarian body, but "parasitic structures," independent, unicellular organisms, which live only as parasites in the body of the Radiolaria (compare § 90).

This important recognition underwent ten years later a further development and complete establishment by the extensive investigations of Karl Brandt (L. N. 38, 39) and Patrick Geddes (L. N. 42, 43). This arrangement was compared by Brandt to the remarkable symbiosis of the Algoid gonidia and Fungoid hyphÆ in the organisation of the Lichens, which had been recently discovered, and since he recognised the independent nature of the yellow cells, as unicellular AlgÆ, in all divisions of the Radiolaria, he founded for them the genus Zooxanthella. Geddes named them Philozoon, and showed experimentally that they give out oxygen under the influence of sunlight (compare § 90). The great physiological importance of the yellow cells in the metastasis of the Radiolaria, and, when they are developed in large quantities, in the economy of marine organisms in general, has recently been insisted upon by Brandt (see § 205 and L. N. 52, pp. 65-71, 86-94).

The proof that the yellow cells do not belong to the Radiolarian organism itself, but only live parasitically in it, was a necessary preliminary to the very important step which next took place in our knowledge of the organisation of the Radiolaria. This step consisted in the demonstration that the whole body of the Radiolaria, like that of all other Protista, is only a single cell. It was Richard Hertwig who in two remarkable works (L. N. 26, 33) firmly established this fundamental theorem of the unicellular nature of the Radiolaria. In his treatise on the histology of the Radiolaria (L. N. 26, 1876) he published complete investigations into the structure and development of the SphÆrozoida and Thalassicollida. Since he made use of the modern methods of histological examination, and especially of staining fluids, which he was the first to apply to the study of the Radiolaria, he was able to show that no true cells (apart from the parasitic yellow cells) are to be found in their bodies, but rather that all their morphological components are to be regarded as differentiated parts of a single true cell, and in particular that the central capsule includes a genuine nucleus.

A wider foundation for this important discovery and its applicability to all divisions of this extensive class, was given by Hertwig in a second work on the organisation of the Radiolaria (L. N. 33, 1879). Among the numerous discoveries by which this work enriched the natural history of the Radiolaria must be specially mentioned the recognition of the fundamental differences exhibited by the main divisions of the class in the structure of their central capsule. Hertwig first observed that the capsular membrane is double in the PhÆodaria but single in the other Radiolaria (§ 56); the former he named "Tripylea" because he discovered in their capsular membrane a large, peculiarly constructed main opening and two small accessory openings. The Nassellaria, in which he found a single porous area at the basal pole of the main axis, with a cone of pseudopodia rising from it, he called on this account "Monopylea"; whilst the other Radiolaria, whose capsular membrane is perforated on all sides with fine pores, were termed "Peripylea." Besides the central capsule, Hertwig laid stress upon the significance of the gelatinous envelope as a constant and important constituent of the body. He also devoted attentive consideration to the morphology of the skeleton, and on the basis of certain phylogenetic conclusions which he drew from it, he arrived at an improved systematic arrangement in which he distinguished six orders:—(1) Thalassicollea, (2) SphÆrozoea, (3) Peripylea, (4) Acanthometrea, (5) Monopylea, (6) Tripylea. The numerous isolated discoveries with which Hertwig enriched the morphology of the Radiolaria, have been already alluded to in the appropriate paragraphs in the anatomical portion of this Introduction (see L. N. 42, pp. 340, 341).

By the discovery that the PhÆodaria, although differing in important respects from the other Radiolaria, still conform to the definition of the class, a new and extensive series of forms was added to this latter, and by their closer investigation a fresh source of interesting morphological problems was disclosed. In other groups, however, morphology was advanced by comparative anatomical studies. In addition to the smaller contributions of various authors, mentioned in the foregoing bibliography, I may specially refer to the valuable BeitrÄge zur Kenntniss der Radiolarien-Skelete, insbesondere der der Cyrtida by O. BÜtschli (L. N. 40, 1882). On the basis of careful comparative anatomical studies, investigations into the skeletal structure of a number of fossil Cyrtoidea and critical application of the recently published researches of Ehrenberg into the Polycystina of Barbados (L. N. 25), BÜtschli attempted to derive the complicated relations of the Monopylean skeletons phylogenetically from a simple primitive form,—the primary sagittal ring. Even if this attempt did not actually solve the very difficult morphological problem in question, still the critical and synthetic mode in which it was carried out deserves full recognition, and furnishes the proof that the comparative anatomy of the skeleton in the Radiolaria not less than in the Vertebrata, is a most interesting and fruitful field of phylogenetic investigation. A further demonstration of this was furnished by BÜtschli in the general account of the organisation of the Radiolaria which he published in 1882 in Bronn's Klassen und Ordnungen des Thierreichs (L. N. 41).

In our knowledge of the developmental history of these Protista the last two decades have witnessed less progress than in their comparative anatomy. The most important advance in this direction has been the proof that in all the main groups of the class the contents of the central capsule are used in the formation of swarm-spores. The movements of these zoospores in the central capsule had indeed been observed by several previous authors in the case of the Spumellaria and Acantharia (L. N. 10, 13, 16; compare also § 142, Note A). The origin of the flagellate spores from the contents of the central capsule and their peculiar constitution were, however, first described fully by Cienkowski in 1871 (L. N. 22, p. 372). Soon after this, R. Hertwig discovered that in the social Radiolaria (Polycyttaria or SphÆrozoea) two different forms of zoospores are formed, one with, the other without crystals, and that the latter are also divided into macrospores and microspores (compare L. N. 26, and § 142). Recently this sexual differentiation has been shown by Karl Brandt to exist in all the groups of SphÆrozoea, and its regular interchange with the formation of crystal-spores has been interpreted as a true "alternation of generations" (compare L. N. 52 and also § 216). The other forms of development also, especially reproduction by cell-division (§ 213) and gemmation (§ 214), have been elucidated by the recent investigations of the same author.

The palÆontology of the Radiolaria has of late made important and interesting advances. Until ten years ago fossil remains of this class were known exclusively from the Tertiary period; almost the only source of our information was to be found in the researches of Ehrenberg, commenced in 1838, continued in his Mikrogeologie in 1854, and concluded in his last work (L. N. 25) published in 1875 (compare L. N. 16, pp. 3-9, 191-193). In the year 1876 a number of Mesozoic Radiolaria from the chalk were described by Zittel (L. N. 28), and afterwards others from the Jura by Dunikowski (L. N. 44). That fossil Radiolaria occur in Mesozoic formations, especially in the Jura, as well preserved and as abundantly as in the Tertiary rocks of Barbados, was shown in 1883 by RÜst (L. N. 48). By the examination of numerous thin sections he discovered that in all the main divisions of the Jurassic formation (Lias, Dogger, Malm) there are distributed jaspers, flints, cherts, and other quartzites, which consist largely of the siliceous shells of Polycystina; the same is true also of many Coprolites found in the Jura. The full account of these and the descriptions and figures of 234 Jurassic species, distributed in 76 genera, are contained in the BeitrÄge zur Kenntniss der fossilen Radiolarien aus Gesteinen des Jura (L. N. 51, 1885). But even in the older rocks, the Trias, the Permian, and Carboniferous systems, and even as far downwards as the Silurian and Cambrian formations, RÜst has recently shown the existence of fossil Radiolaria, and thus increased the known period of the developmental history of the class by many millions of years (§ 244).

The great significance of the Radiolaria in geology and palÆontology has been brought into new light not only by these extensive discoveries, but also by the important relations which have been shown to exist between the Radiolarian rocks and the deep-sea deposits of the present day. In this direction the wonderful discoveries of the Challenger, and especially the investigation of the deep-sea deposits by Wyville Thomson (L. N. 31) and John Murray (L. N. 27), have furnished us with new and valuable information (compare §§ 236-239, and §§ 245-250). The Tertiary Polycystine formations of Barbados and the Nicobar Islands, with which we have been acquainted for the last forty years, as also the Mesozoic Radiolarian quartzes, which have only recently been made known to us from the Jura, are ascertained to be fossil representatives of the same deep-sea deposits which now occur in the form of Radiolarian ooze (§ 237), and to some extent also of Globigerina ooze and red clay (§§ 238, 239), on the bottom of the ocean, at depths of from 2000 to 4500 fathoms.

Ehrenberg himself, towards the end of his long and laborious life, collected the results of the systematic and palÆontological researches, which he had begun thirty-seven years previously (L. N. 16, pp. 3-12) into the Polycystina, in two large works (L. N. 24, 25). The first treatise (L. N. 24, 1872) contains the Mikrogeologische Studien Über das Kleinste Leben der Meeres-TiefgrÜnde aller Zonen und dessen geologischen Einfluss, with a list of 279 Polycystina observed by him from the deep-sea, as well as figures of 127 species. The second work (L. N. 25, 1875) contains the Fortsetzung der Mikrogeologischen Studien, mit specieller RÜcksicht auf den Polycystinen-Mergel von Barbados; the list of fossil Polycystina observed by him includes 325 species, of which 26 are still extant; 282 of them are figured on the thirty plates accompanying the memoir. By means of these numerous figures, as well as by the appended systematic and chorological tables, Ehrenberg furnished a welcome supplement to the numerous communications regarding the Polycystina, which he had made to the Berlin Academy since 1838, and which he had published in his Mikrogeologie in 1854. It will always be the merit of this zealous and indefatigable microscopist that he first called attention to the great wealth of forms existing in this class; he separated systematically about 500 species, and published drawings of about 400; in addition to which he was the first to lay stress upon the great chorological and geological importance of the Radiolaria.

With these systematic and descriptive, chorological and palÆontological works, however, which relate exclusively to the Polycystina, the merits of the famous naturalist of Berlin are exhausted as regards this class of animals. Of the organisation of the Radiolaria, Gottfried Ehrenberg remained entirely ignorant up till his death in 1876. All that a number of famous naturalists had observed during a quarter of a century as to the structure and life-history of the Radiolaria, all the important discoveries of Huxley (1851), Johannes MÜller (1858), ClaparÈde (1858), Cienkowski (1871), and many others (L. N. 1-22), and all that I had published in my Monograph (1862) on the basis of three years' study of their anatomy and physiology—all this Ehrenberg ignored, or rather, he regarded it all as worthless rubbish of science, as a chaos of devious errors, resting upon incomplete observations and false conclusions. His strange "special considerations regarding the Polycystina" (L. N. 24, pp. 339-346) and the general "concluding remarks" (L. N. 25, pp. 146-147) leave no room for doubt on this point. Ehrenberg indeed doubted to the last whether any observer had seen living Radiolaria at all (L. N. 25, p. 108).

The invincible obstinacy with which Ehrenberg maintained his preconceived opinion of the high organisation of the Radiolaria, and entirely ignored the contrary observations of other naturalists, is explained by the consistency with which he held to the end the "principle peculiar to himself of the universally equal development of the animal kingdom" (L. N. 16, p. 7). From the complicated arrangement of their siliceous shells he concluded that the animals inhabiting them must possess a structure correspondingly complex, and nearly related to that of the Echinodermata (Holothuria). Like all other animals the Radiolaria must possess systems of organs for locomotion, sensation, nutrition, circulation, and reproduction. Whilst Ehrenberg originally interpreted the Polycystina as siliceous Infusoria polygastrica, and regarded them as compound Arcellina, he afterwards classed them sometimes with the Echinodermata (Holothuria), sometimes with the Bryozoa, sometimes with the Oscillaria (see L. N. 41, p. 336). Although a decided opponent of the cell-theory he called them "multicellular animalcules" (Polycystina), interpreting the pores of the siliceous shell as cells. To-day the opposite term (Monocystina) might be adopted to express their unicellular organisation. It was a remarkable irony of fate that in the self-same year (1838) in which Schwann of Berlin made by his foundation of the cell theory the greatest advance in the whole of Biological Science, that Ehrenberg, all his life the most zealous opponent of that theory, published his great work on the Infusoria, and at the same time established the "family of multicellular animalcules or Polycystina" (L. N. 16, p. 4).

The "short systematic survey of the genera of cellular animalcules" given by Ehrenberg in 1875 (L. N. 25, p. 157), is only a new edition, increased by sixteen genera, of his first systematic arrangement of the Polycystina of 1847 (L. N. 4, p. 53). Since I have already given a full discussion of this in my Monograph (L. N. 16, pp. 214-219), I need only here remark that a correct understanding of his very inadequate generic diagnoses is only possible by the aid of his figures. Relying upon these I have retained almost all Ehrenberg's genera, although entirely new definitions of most of them have been necessary.

The same is true also of the two orders which Ehrenberg distinguished in his class of "Zellenthierchen." The first order is constituted by his "NetzkÖrbchen" (Monodictya or Nassellaria) formerly known as "Polycystina solitaria"; they include our Cyrtoidea, the greater part of Hertwig's Monopylea. Ehrenberg's second order is the "Schaumsternchen" (Polydictya or Spumellaria), previously called "Polycystina composita"; they include the Peripylea of Hertwig, as well as the Spyridina (our Spyroidea), which belong properly to the Nassellaria. Although Ehrenberg's statements regarding the organisation of both these orders were quite erroneous, and his knowledge even of the structure of their shells very defective, I still thought it advisable to retain his names for the groups, since they constituted his one successful effort in the systematic treatment of the Radiolaria (compare L. N. 41, p. 336).

The sketch of a systematic arrangement of the Radiolaria (L. N. 37), which I published in 1881 on the basis of the study of the Challenger Radiolaria, resembles, in respect of seven orders being distinguished, the new system which R. Hertwig founded in 1879, in consequence of the variations which he discovered in the structural relations of the central capsule (L. N. 33, p. 133). It differs, however, inasmuch as his SphÆrozoea (my Polycyttaria) are here divided into two orders, Symbelaria (CollosphÆrida) and Syncollaria (SphÆrozoida). In that sketch too I separated for the first time the two subclasses Holotrypasta (Porulosa) and Merotrypasta (Osculosa). The fifteen families established by Hertwig were then raised to twenty-four. The six hundred and thirty genera, which I then distinguished, are still for the most part retained, some, however, in a restricted sense, or with amended definitions.

The differential characters of the orders and families of the Radiolaria, given in the Prodromus in 1881, were amended in a further communication which I gave in 1883 regarding the orders of the Radiolaria (L. N. 46, p. 17). There I reduced the seven orders to four, the structural relations of the central capsule being precisely the same in the Polycyttaria and Collodaria as in the Peripylea. The survey of the affinities of the class was thus rendered much simpler and clearer, and the hypothetical genealogical tree, which I then published, has been still further carried out in Chapter VI. of the present Introduction (see §§ 153-200).

253. General Survey of the Growth of our Systematic Acquaintance with the Radiolaria from 1834 to 1885.

1834. Meyen (L. N. 1) describes 2 genera and species of Collodaria:—SphÆrozoum fuscum and Physematium atlanticum.

1838. Ehrenberg (L. N. 2) founds the family Polycystina upon 3 fossil genera (with 6 species):—Lithocampe, Cornutella, Haliomma.

1847. Ehrenberg (L. N. 4) publishes his preliminary communications regarding the fossil Polycystina of Barbados and distinguishes 282 species, distributed in 44 genera and 7 families. In the tabular view of the genera he distinguishes two orders:—I. Solitaria—(1) Halicalyptrina, (2) Lithochytrina, (3) Eucyrtidina; and II. Composita—(4) Spyridina, (5) Calodictya, (6) Haliommatina, (7) Lithocyclidina (compare L. N. 16, pp. 214-219).

1851. Huxley (L. N. 5) gives the first accurate account of living Radiolaria, and describes 2 species of the genus Thalassicolla (nucleata and punctata); under the latter are included 4 genera of SphÆrozoea:—Collozoum, SphÆrozoum, CollosphÆra, SiphonosphÆra (compare L. N. 16, pp. 12-14).

1854. Ehrenberg (L. N. 6) publishes in his Mikrogeologie, figures of seventy-two species of fossil Polycystina (without descriptions).

1855. Johannes MÜller (L. N. 8, p. 248) describes the first Acanthometra, and elucidates its affinity to Huxley's Thalassicolla and Ehrenberg's Polycystina.

1858. Johannes MÜller (L. N. 12) establishes the new group Radiolaria as a special order of the Rhizopoda, and includes in it the Thalassicolla, Polycystina, and Acanthometra as closely related families. He opposes these radiate Rhizopoda to the Polythalamia, and describes 50 species observed by him living in the Mediterranean, these he arranges in 20 genera, of which 10 are new. The figures are contained in eleven plates (see L. N. 16, pp. 22-24).

1858. ClaparÈde (L. N. 14) describes the first Plectoidean (Plagiacantha arachnoides) and two species of Acanthometra, which he had observed living in Norway (see L. N. 16, p. 18).

1860. Ehrenberg (L. N. 4) gives a short diagnosis of 22 new genera of Polycystina, based on the investigation of numerous deep-sea species brought up by Brooke from the depths of the Pacific Ocean. The number of his genera is thus increased to 66 (compare L. N. 16, pp. 10, 11).

1862. Ernst Haeckel (L. N. 16) embraces in his Monograph of the Radiolaria all the species hitherto known either by figures or descriptions, and arranges them in 15 families and 113 genera; of which latter 46 are new. The number of new species observed living amounts to 144. In a "survey of the Radiolarian fauna of Messina" (p. 565) he records 72 genera and 169 species. Most of these are figured in the accompanying atlas of thirty-five plates.

1862. Bury (L. N. 17) gives in an atlas of twenty-five plates, photographed from drawings, the figures of numerous fossil Polycystina of Barbados (without descriptions), of which many are new species overlooked by Ehrenberg (compare § 242, above).

1872. Ehrenberg (L. N. 24) gives a list of names (without description) of all the Polycystina observed by him from the bottom of the sea, 279 species, of which 127 are figured on twelve plates.

1875. Ehrenberg (L. N. 25) gives a list of names of all the fossil Polycystina observed by him (from Barbados, the Nicobar Islands and Sicily), 326 species, of which 282 are figured (compare § 242 above). In a new "Systematic Survey of the Genera" the number of these is given as 63. The 7 families are the same as given in 1847 (see above), as also the two orders (Nassellaria = Solitaria, Spumellaria = Composita).

1876. Zittel (L. N. 29) describes the first fossil Radiolaria from the chalk (6 species) and establishes the new Cyrtoid genus Dictyomitra.

1876. John Murray (L. N. 27) establishes the new family Challengerida, and figures 6 new generic types of PhÆodaria.

1879. Richard Hertwig (L. N. 33) first describes the fundamental differences in the structure of the central capsule, and in accordance with them divides the Radiolaria into six orders:—(1) Thalassicollea, (2) SphÆrozoea, (3) Peripylea, (4) Acanthometrea, (5) Monopylea, (6) Tripylea (p. 133). These are subdivided into 18 families, and their phylogenetic affinities discussed (p. 137). On the ten plates, several new species from Messina are figured, among them the types of several new genera (Cystidium, Coelacantha, EchinosphÆra) (compare § 252).

1879. Ernst Haeckel (L. N. 34) founds the order PhÆodaria as a "new group of marine siliceous Rhizopods," and distinguishes in it 4 suborders, 10 families and 38 genera.

1880. Emil StÖhr (L. N. 35) describes the Miocene "Radiolarian fauna of the tripoli from Grotte in Sicily," 118 species, of which 78 are new; among them is the new genus Ommatodiscus, the type of a new family, Ommatodiscida. The new species are figured on seven plates.

1880. Dante Pantanelli (L. N. 36) describes 30 species of fossil Polycystina from the jaspers of Tuscany, which he regarded as Eocene, but which were probably of Jurassic origin (compare § 243, note B, above).

1881. Ernst Haeckel (L. N. 37) publishes a "Sketch of a classification of the Radiolaria on the basis of the study of the Challenger Collection," and distinguishes in his "conspectus ordinum" (p. 421) 2 subclasses and 7 orders, and in the "prodromus systematis Radiolarium" (pp. 423-472) 24 families with 630 genera, among which are more than 2000 new species.

1882. BÜtschli (L. N. 40) on the basis of studies of the fossil Monopylea of Barbados, investigates the "mutual relations of the Acanthodesmida, Zygocyrtida and Cyrtida," and gives a critical revision of the genera of these "Cricoidea;" a number of new species are described and figured (Tafs. xxxii., xxxiii.), and some new genera of Stichocyrtida established (Lithostrobus, Lithomitra, &c.).

1882. Dunikowski (L. N. 44) describes 18 new fossil Polycystina from the lower lias of the Salzburg Alps, among them the types of 3 new genera (Ellipsoxiphus, TriactinosphÆra, and Spongocyrtis).

{clxxxviii}

1883. Ernst Haeckel (L. N. 46) revises the 4 orders and 32 families of Radiolaria, and gives more accurate definitions of them, as well as of the 2 subclasses (I. Holotrypasta = Acantharia and Spumellaria; II. Merotrypasta = Nassellaria and PhÆodaria).

1885. D. RÜst (L. N. 51) describes 234 new species of fossil Radiolaria from the Jura, and illustrates them by twenty plates. Among them are 103 Spumellaria, 130 Nassellaria, and 1 PhÆodaria; these are contained in 35 genera, of which 20 belong to the Porulosa, and 15 to the Osculosa.

Note.—In the tenth and eleventh columns the relative abundance of each order at or near the surface and near the bottom is approximately indicated by the letters A-E, which have the following significance:—A, abundant; B, very numerous; C, many (medium quantity); D, few; E, very few.

SYSTEMATIC PART.

Class RADIOLARIA.

Radiolaria, Johannes MÜller, 1858.

Rhizopoda radiaria, Johannes MÜller, 1858.

Polycystina (pro parte), Ehrenberg, 1838.

Echinocystida, ClaparÈde, 1858.

Rhizopoda capsularia, Haeckel, 1861.

Cytophora, Haeckel, 1862.

Definition of the Class:—Rhizopoda with unicellular body, divided by a porous membrane into an internal or intracapsular part (with nucleus), and an external or extracapsular part (with calymma); propagating by flagellated spores.

The Radiolaria or Capsulate Rhizopoda, first constituted by Johannes MÜller in the year 1858 as a separate group of the Rhizopoda, form a peculiar class of the Protista, or unicellular organisms. This class is exclusively marine, and has in general the characteristic organisation of the Rhizopoda, with the development of numerous pseudopodia from the surface of the cell; but it differs from all other Rhizopoda in the possession of a peculiar membrane, dividing the cell-body into two different parts; the central capsule or the internal part with the nucleus, and the external part or extracapsulum with the calymma; propagation by flagellated spores produced in the central capsule; the sarcode or the protoplasm of both parts communicates by fine pores, piercing the separating membrane, which is called the capsule-membrane.

The Central Capsule or the inner part of the Radiolarian body is constantly composed of three essential parts, viz.:—

1. The Central Nucleus (a true cell-nucleus).

2. The Intracapsular Sarcode (endosarc) or surrounding internal protoplasm.

3. The Capsule Membrane or enveloping porous membrane.

Besides these constant and essential elements, the central capsule contains very commonly (but not constantly) some other enclosed structures, viz.:—

4. An internal or intracapsular skeleton.

5. Intracapsular vacuoles or alveoli.

6. Fat-granules or oil-globules.

7. Crystals of different composition.

8. Pigment-granules.

The Extracapsulum, or the outer part of the Radiolarian body is also constantly composed of three essential elements,—

1. The Calymma, or the thick extracapsular jelly-veil, completely enveloping the whole central capsule.

2. The Matrix, or the maternal tissue of the external protoplasm, enveloping immediately the capsule-membrane as a thin continuous layer of extracapsular sarcode (ectosarc).

3. The Pseudopodia, or the very numerous thread-like filaments of protoplasm, which radiate from the matrix; whilst their inner part is enclosed in the calymma, their outer part floats freely in the sea-water.

Besides these three constant and essential elements, the extracapsulum contains very commonly (but not constantly) some other enclosed structures, viz.:—

4. An external or extracapsular skeleton.

5. Extracapsular vacuoles or alveoli.

6. Fat-granules or oil-globules.

7. Pigment-granules or a peculiar large body of dark extracapsular pigment, the "phÆodium."

8. "XanthellÆ" or "zooxanthellÆ," peculiar yellow cells, which contain starch and are unicellular yellow AlgÆ, living as "Symbiontes" in true Symbiosis with a great many Radiolaria.

The Nucleus of the Radiolaria is a large true simple cell-nucleus, originally a solid spherical, roundish or longish body of nuclein. It is placed either in the centre of the capsule (in most Peripylea) or excentrically (in most other Radiolaria). Originally solid, the nucleus is commonly differentiated later into an outer dense nuclear-membrane and an inner softer or fluid content; either with one single nucleolus or with a variable number of nucleoli. Originally always simple, the nucleus becomes afterwards constantly divided into numerous small nuclei, each of which, together with a part of the surrounding protoplasm, forms a vibratile-spore or "flagellate-spore." This division in the Acantharia and in the social (or colonial) Peripylea begins very early, in all other Radiolaria much later, immediately before propagation.

The Endoplasm or "endosarc," or "intracapsular protoplasm" or "inner sarcode," in all Radiolaria originally fills that space within the capsule, which is not taken up by the nucleus. It seems to be employed mainly for the purpose of propagation, becoming divided earlier or later into numerous small particles, each of which surrounds a small particle of the nucleus and forms together with it a flagellate-spore. Besides this the endoplasm of the Radiolaria seems to have a great significance for the nutrition, mainly for the interchange of materials. It becomes very often vacuolate or alveolate, filled with smaller or larger spherical drops of fluid; it produces very commonly smaller fat-granules or larger oil-globules, and further pigment-granules of different colours, more rarely crystals and other peculiar enclosed parts.

The Membrane or "capsule-membrane" is the most typical and characteristic part of the body of a Radiolarian, sufficient of itself to separate this class from all other Rhizopoda. At the same time, by its different shape it presents the best means for the systematic distinction of the four subclasses or "legions" of the class. The membrane is composed of a special organic matter (probably nearly related to chitin) and combines density with elasticity to a high degree. Observed with a high power of the microscope its margin (or section) appears commonly simple-edged, but often in larger forms distinctly double-edged.

The legion PhÆodaria is distinguished by a double membrane (the thinner inner and thicker outer membranes being separated by an interval); in the three other legions it is simple. The membrane completely separates the intracapsular from the extracapsular body, both communicating only by certain pores or openings in the membrane. With reference to this important communication, the whole class can be divided into two subclasses, Holotrypasta and Merotrypasta: the Holotrypasta contain the Peripylea and Actipylea, in which the membrane is pierced by innumerable very small pores; the Merotrypasta consist of the Monopylea and the Cannopylea, in which the membrane exhibits only one large main opening, distinguished in the former by a peculiar "porous area," in the latter by an "osculum" or a prolonged tubule.

The Calymma or "jelly-veil" is the most characteristic part of the extracapsular body in all Radiolaria; in the majority of the class it is the most voluminous part of the whole body, being much more voluminous than all the other parts taken together. The calymma is a structureless, clear, and transparent jelly-envelope which always includes the whole central capsule and often also the whole extracapsular skeleton. Owing to the high degree of its consistence, this jelly-veil takes a very important part in the formation of the extracapsular skeleton, furnishing the matrix for the deposition of its tangential parts.

The Matrix or the "maternal tissue of the pseudopodia" is formed in all Radiolaria by the thin layer of exoplasm or of extracapsular sarcode, which immediately envelops the central capsule and is itself enclosed by the calymma. This continuous sarcode-cover of the capsule communicates by its pores or openings with the endoplasm or the intracapsular sarcode; whilst from its outer surface arise the pseudopodia. The morphological signification of the matrix is very small, but the physiological importance is very great, for it seems to be the chief organ of many vital functions.

The Pseudopodia or the very fine, long, thread-like filaments of exoplasm arise in all Radiolaria in very great numbers from the surface of the matrix, and exhibit in general the same characteristic shape as in the other Rhizopoda. Their inner or proximal part is enclosed within the jelly-veil or calymma, whilst their outer or distal part floats freely in the sea-water. Their special motions and modifications exhibit considerable variations in different groups, their tendency to ramify, anastomose, and form networks being in some cases very small, in others very great. Also the characteristic motion of granules in the pseudopodia is very different. In general those most important exoplasmatic filaments serve as organs both for the vegetative functions of nutrition, and for the animal functions of motion and sensation.

The class Radiolaria can be divided according to its varying structure into four different legions or subclasses, the characters of which are the following:—

I. PERIPYLEA or SPUMELLARIA.

Membrane of the central capsule simple, perforated by innumerable very fine pores. Fundamental form originally homaxon or spherical. Skeleton wanting or siliceous. No phÆodium in the extracapsular calymma. The Peripylea comprise two orders:—

A. Collodaria (without lattice-shell).

B. SphÆrellaria (with lattice-shell).

II. ACTIPYLEA or ACANTHARIA.

Membrane of the central capsule simple, perforated by innumerable fine pores. Fundamental form originally homaxon or spherical. Skeleton acanthinic (not siliceous). No phÆodium in the extracapsular calymma. The Actipylea consist of two orders:—

A. Acanthometra (without complete lattice-shell).

B. Acanthophracta (with complete lattice-shell).

III. MONOPYLEA or NASSELLARIA.

Membrane of the central capsule simple, perforated by a porous-area, or by one single large opening, divided into numerous very fine pores. Fundamental form originally monaxon or egg-shaped. Skeleton siliceous. No phÆodium in the extracapsular calymma. The Monopylea comprise two orders:—

A. Plectellaria (without complete lattice-shell).

B. Cyrtellaria (with complete lattice-shell).

IV. CANNOPYLEA or PHÆODARIA.

Membrane of the central capsule double, perforated by one simple main-opening, prolonged into a tubulus, and besides this commonly by one or two (rarely more) small accessory openings. Fundamental form originally monaxon or egg-shaped. Skeleton siliceous. Constantly a peculiar dark pigment-body or "phÆodium" in the extracapsular calymma. The Cannopylea comprise two orders:—

A. PhÆocystina (without lattice-shell).

B. PhÆocoscina (with lattice-shell).

Synopsis of the four Subclasses or Legions of Radiolaria.

A. HOLOTRYPASTA. B. MEROTRYPASTA.
Central capsule everywhere perforated by innumerable small pores. Central capsule with one large main-opening (with or without small accessory openings).
Fundamental form originally homaxon (spherical or derived from a sphere). Fundamental form originally monaxon (egg-shaped or perhaps dipleural).
I. II. III. IV.
Spumellaria. Acantharia. Nassellaria. PhÆodaria.
(Peripylea.) (Actipylea.) (Monopylea.) (Cannopylea.)
Wall-pores of the capsule equally disposed. Wall-pores of the capsule symmetrically disposed. Main-opening of the capsule with a porous operculum. Main-opening of the capsule with a short tubule.
Skeleton siliceous or wanting. Skeleton acanthinic (organic). Skeleton siliceous (rarely wanting). Skeleton siliceous (rarely wanting).
Calymma without phÆodium. Calymma without phÆodium. Calymma without phÆodium. Calymma constantly with a phÆodium.
                                                                                                                                                                                                                                                                                                           

Clyx.com


Top of Page
Top of Page