No person can derive advantage from the study of parasites unless the subject be approached in a right frame of mind. In other words, the student of helminthology must, as a primary discipline, dispossess himself of all preconceived opinions whatsoever, and in an attitude of child-like simplicity seek truth for its own sake. Unless the mind be absolutely free and unfettered it cannot rightly interpret the facts of this peculiar department of biological science. Those students who are nervously anxious to reconcile the conclusions of modern science with the ideas of their forefathers are certain to remain just as ignorant of the true value and significance of nature-teachings as all their fathers were.

Whether dealing with the external or internal forms, the study of parasites of man and animals is practically one of boundless extent; and there is probably no department of knowledge, possessing an equal value in relation to the welfare of man and beast, that is so thoroughly misunderstood by those who are directly concerned in the appreciation of its revelations. This has arisen from a total misconception as to cause and effect. Most people, not excluding even the votaries of the healing art, following tradition, regard the internal parasites or entozoa as creatures either directly resulting from certain diseased conditions of their hosts or as organisms which would not have existed if their bearers had been perfectly healthy. Nothing can be more absurd. Such a conclusion is utterly at variance with all logical deduction from known facts. It is, however, quite on a par with multitudes of other popular delusions which, in spite of the advance of science, will probably never become wholly eradicated from the public mind. People who hold these notions either cannot or do not desire to reject a view which has for them a dominating power almost equal to that of any known religious dogma. In conversation I have repeatedly noticed this to be the case. These people are the victims of educated ignorance and they will never allow that parasites are natural developments, accomplishing ends or parts of the orderly mystery which reigns everywhere. Some of then still cling to the creed that the presence of parasites, of internal ones at least, betokens evidence of Divine disfavor; and their minds are troubled with all sorts of distressing and childish conceptions. In the present age one would have thought that such ridiculous ideas could not be seriously maintained; but instead of being relegated to the limbo of similar “old wives’ fables” they dominate the opinions of thousands of our so-called educated people. The genuine searcher after truth does not need to be told that all preconceptions of this order hopelessly obscure the mental vision. They operate to render a just and adequate understanding of the science of helminthology impossible. The biologist may say what he lists, but he knows perfectly well that the superstitious mind will continue to ignore the precious and elevating results of scientific research, and that it will perseveringly continue to persuade itself that internal worms, parasites, and entozoa, of whatever kind, belong to the category of “plagues” liable to be distributed as special punishments for human wrong-doing.

As remarked in my previous treatise, the best way of studying the entozoa is to regard them as collectively forming a peculiar fauna, destined to occupy an equally peculiar territory. That territory is the wide-spread domain of the interior of the bodies of man and animals. Each bearer or “host” may be viewed as a continent, and each part or viscus of his body may be regarded as a district. Each district has its special attractions for particular parasitic forms; yet, at the same time, neither the district nor the continent are suitable as permanent resting-places for the invader. None of the internal parasites “continue in one stay;” all have a tendency to roam; migration is the soul of their prosperity; change of residence the essential of their existence; whilst a blockade in the interior soon terminates in degeneration and death. I repeat it. The entozoa constitute a specialised fauna. What our native country is to ourselves, the bodies of animals are to them. To attack, to invade, to infest, is their legitimate prerogative. Their organisation, habits, and economy are expressly fashioned to this end. How remarkable and complex is their structure, and how peculiar, diverse, and varied are their ways and wanderings, the contents of this volume will, I trust, sufficiently explain. The puerile horror which even some scientific persons affect to display in regard to the subject is altogether out of place. To the rightly balanced mind the study of these much abused “worms” is just as attractive as any other section of zoology. Helminthology opens up to our view many of the strangest biological phenomena of which the human mind can take cognisance; whilst a profound and extended knowledge of the subject, in all its bearings, is calculated to secure to the community a rich practical reward by enabling us to do effectual battle with not a few of the many ills of life to which our flesh is heir.

Further on the general advantages to be derived from the study of parasites I cannot here dilate, and it becomes the less necessary that I should do so, since I have entered upon the subject very fully elsewhere. The character of the present work, moreover, imposes brevity. If the plan which I now propose to follow should not be deemed altogether satisfactory from the purely zoological standpoint, it will nevertheless have the advantage of simplicity and novelty; and knowing full well the difficulties that must surround any attempt to give a perfect classification of the entozoa, considered as a natural group, I feel sure that my helminthological friends will credit me with exercising a wise discretion in selecting the simplest available method of arrangement. My plan, therefore, is to devote separate sections of this work to the parasites of the different classes of vertebrated animals, including man, treating of the various species in regular succession. This arrangement is merely one of convenience and has no reference whatever to conceptions of zoological equivalency as variously interpreted and maintained by authors and investigators. The parasitic groups will be taken up in the following order, quite irrespective of their relative importance, and also without any attempt to treat each group with equal fulness. In the matter of recent literature only will the present record and summary make any approach toward completeness, my hope being to render this treatise indispensable and trustworthy as a ready means of reference.

I. Flukes. Trematoda.—This group embraces several families of parenchymatous worms. The various species exhibit one or more suckers, which the older naturalists regarded as so many mouths or perforations. Hence the ordinal title. The term fluke is of Saxon origin, meaning anything flat. Thus, it has been applied to sole-fish or flounders, to the flattened halves of the tail of cetaceans, to the blades of anchors, and so forth. Although the common liver fluke is flat, many species of the order are round, biconvex, or even filiform organisms. I recognise six families:—MonostomidÆ, DistomidÆ, AmphistomidÆ, TristomidÆ, PolystomidÆ, and GyrodactylidÆ. Most of the species are entozoal; but many adhere to the surface of the body of piscine hosts.

II. Tapeworms. Cestoda.—This comprises not only the tapeworms, but also the measles and other bladder-worms or cystic Entozoa of the old authors (Cystica). The Greek word kestos means a band or girdle; hence the ordinal term above given. The bladder-worms, including Hydatids, Cysticerci, &c., are the larval stages of growth of various tapeworms. The further reduction of this order into sub-orders or families requires careful attention. At present we have TÆniadÆ, AcanthotÆniadÆ, DibothridÆ (= BothriocephalidÆ), DiphyllobothridÆ, TetrarhynchidÆ, and TetraphyllobothridÆ. All the genera and species are entozoal. The proposal to separate the snouted or proboscidiform tapeworms (RhynchotÆniadÆ) from those in which the rostellum is absent (ArhynchotÆniadÆ) does not recommend itself to my judgment.

III. Roundworms. Nematoda.—This series comprises not only lumbricoid or roundworms proper, but also threadworms. The term derives its origin from the Greek word nema, signifying a thread. It likewise includes the strongyles, the term strongulos meaning round or cylindrical. This is a very extensive group whose parasitic members are strictly entozoal, whilst the non-parasitic forms are either entirely free or they infest plants. Some of the so-called free nematoids live in the slime of animals. The artificial classification by Schneider, based on the muscular system, places these parasites in three well-marked groups, but I think it a disadvantage to separate widely many really closely allied forms. Thus, in his Polymyarii we have the genus Enstrongylus, and in his Meromyarii the Strongyli proper. Most of the genera may be fairly included in the following families:—AscaridÆ, CheiracanthidÆ, CucullanidÆ, StrongylidÆ, TrichinidÆ, OxyuridÆ, TrichocephalidÆ, FilaridÆ, GordiidÆ, AnguillulidÆ.

IV. Thornheaded-worms. Acanthocephala.—This group embraces a small series of parasites, which, in general appearance, resemble the nematode worms. They differ, however, essentially, being, as the term indicates, furnished with spine-covered heads. They are, moreover, destitute of digestive organs. The species are entozoal in habit, abounding particularly in fishes and reptiles. At present, all the known forms are included in one family (EchinorhynchidÆ), which also comprises only a single genus.

V. Annelid Parasites. Suctoria.—In this category one must place all such suctorial annelids as affix themselves to hosts for a longer or shorter period. Many of the leech-like parasites (ClepsinidÆ, and especially MalacobdellidÆ) remind one of certain flukes (Tristoma, &c.) possessing ectozoal habits; whilst the leeches, properly so called, afford instances of the passage from a semi-parasitic to what has been called the free parasitic mode of existence. In tropical countries these creatures very readily attach themselves to man and animals, often creating severe distress. The genera Clepsine and HÆmocharis attack mollusks and fishes respectively. The species are all ectoparasitic and exceedingly numerous. They cannot be described in this work.

VI. Arachnid parasites, Arachnida (part of).—The great class of articulated, limb-jointed, or, more strictly, arthropodous animals, includes a variety of parasites. The mites, true ticks, and such like creatures, belong to this group. Some few of them are entozoal in habit, others are only partially so, whilst the majority are entirely ectozoal. Of the two great sections of Arachnida, namely, Pulmonaria and Trachearia, the latter alone contains strictly parasitic forms. The parasitic species belong to the following families:—PentastomidÆ, PycnogonidÆ, IxodidÆ, AcaridÆ, GamasidÆ, HydrachnidÆ, SolpugidÆ. The parasitism of some of the species is very partial or slight. Thus, certain of the water mites, in their juvenile state, dwell on aquatic insects only; and the tick-like GamasidÆ occur upon dung-beetles. The other ectozoal species attack vertebrated animals, and several attach themselves to man himself. The whale lice (CyamidÆ) are here included in the PycnogonidÆ, though often placed by zoologists with the Crustaceans.

VII. Crustacean Parasites. Crustacea (part of).—A large number of species belonging to various well-marked sections of this great class of Invertebrates are parasitic in their habits, most of them being comprised in the so-called haustellated group. They are familiarly known to zoologists as Epizoa. As this latter term implies, they are strictly ectozoal in character, most of the species victimising fishes by attaching themselves, not only to the general surface of the body, but also to the eyes, and especially to the gills or branchiÆ. The species for the most part belong to the families LernÆidÆ, CaligidÆ, DichelestidÆ, and ArgulidÆ. In this category must likewise be placed two other families belonging to the so-called isopodous section of edriophthalmatous crustaceans. These are the CymothoidÆ, which attach themselves to the tails of fishes, and the BopyridÆ, which occupy the branchial cavity of shrimps. The nature of this work precludes any detailed notice of the numerous members of this section.

VIII. Insect Parasites. Insecta (part of).—The insects, properly so called (that is to say, arthropodous, evertebrated creatures, with six legs), are many of them essentially parasitic in their habits. The most important of these are “bots” and other larvÆ or maggots of various flies (Diptera). The varieties of lice are also included in this group. Some few of the insect parasites are strictly entozoal in habit, at least for a part of their lifetime, being previously attached externally for a short period only. Most of the forms are essentially ectozoal. A very large number of insect tormentors, although deriving nourishment from their victims, attach themselves to the animals for so short a time that they cannot be classed as parasites under the ordinary acceptation of the term. As examples of the so-called free parasitism, the autumnal flies (TabanidÆ) and Stomoxys may be cited. Although embracing but few strictly parasitic forms we have the following:—ŒstridÆ, HippoboscidÆ (with Melophagus), and NycteribiidÆ. In regard to the maggots of MuscidÆ and SarcophagÆ, some of them are parasitic on animals and man, whilst others are parasitic upon insects themselves. The larvÆ of ConopidÆ attack humble-bees internally. Those parasitic insects, properly so called, which, like certain of the crustaceans, are sometimes spoken of as epizoa, comprise three well-marked families. Thus, we have PediculidÆ (the source of lousiness), PhilopteridÆ, and LiotheidÆ. Both of the latter embrace numerous species which for the most part content themselves with devouring the feathers of birds and the hairs of quadrupeds. In addition to these it may be added that some of the rat-tailed larvÆ or Helophilus maggots (SyrphidÆ) are parasitic in man and quadrupeds, as are also the larvÆ of the churchyard beetle (BlaptidÆ). The closely allied TenebrionidÆ and other coleopterous families also supply various maggots possessed of parasitic habits. Fleas and bugs come under Van Beneden’s category of free parasites. This is equivalent to calling them non-parasitic parasites, an expression which looks very like a contradiction of terms.

IX. Protozoal Parasites. Protozoa (part of.)—This miscellaneous assemblage of minute creatures embraces a number of parasites of very low organisation. In the present work it is neither desirable nor necessary to hazard any statements respecting their precise zoological position. It is sufficient to say that the parasitic protozoa are for the most part entozoal in habit, not a few of them possessing vegetable affinities. The microscopic BacteridÆ, GregarinidÆ, and PsorospermiÆ, comprise a multitude of organisms which are strictly parasitic in their habits, whilst amongst the Infusoria we find numerous forms which, though dwelling in the intestinal canal of their hosts, do not derive nourishment in a direct manner from their bearers. Of this kind are Paramecium and Balantidium. The separation of the psorospermiÆ and gregarinÆ into genera is attended with difficulty; nevertheless, I have for convenience long recognised various types under titles corresponding with the names of the observers who first discovered them (Hesslingia, Gubleria, Lindermannia, and so forth). Of necessity, the protozoal parasites will only be incidentally noticed in this work. In this category I place the falsely so called “cattle-plague bodies.” The micrococci and bacteria hardly come within the province of the helminthologist.

Without prejudice to the foregoing restrictions I must at the same time observe that the varied characters presented by the above-mentioned groups show how impossible it is to treat the subject of parasitism adequately, if one is obliged to confine his remarks to the internal parasites or helminths proper. Many creatures possessed of entozoal and ectozoal habits are parasites in every legitimate sense of the term, and yet they do not belong to the class Helmintha in its common zoological acceptation. That class taken by itself may still be allowed to stand pretty much as I represented it in 1864; but in the present work I cease to speak of the Entozoa as in any sense the zoological equivalent of the Helmintha. I prefer to employ the term Entozoa in its popular and wider acceptation. It conveniently stands thus, moreover, in direct contradiction to the term Ectozoa.

As this work treats of parasites only, I purposely refrain from dealing with the Turbellarians, and certain other creatures usually classed with Vermes. The vague term “worms,” so often employed as the equivalent of Helmintha, is misleading in many ways. I should like to see it adopted only when speaking of the Annelids proper. It would still have a sufficiently wide application, seeing that it would include Leeches, Earth-worms, Naids, Tubed-worms, Sea-lobworms, Sea-mice, Nereids, and a host of other setigerous species. Notwithstanding the remote connection subsisting between “intestinal worms” and worms properly so called, the notion that an intimate relation subsists between the lumbricoid helminths and earth-worms will probably never entirely disappear from the popular or even from the professional mind.

Since one of the principal features of this treatise is to afford a handy means of reference to the rich and extended literature of parasitism, I here subjoin a list of general and systematic treatises. To most of these I shall constantly refer. Full special references to detached memoirs will appear in the bibliographies scattered throughout the body of the work.

Bibliography (No. 1).—Bremser, ‘Ueber lebende WÜrmer im lebenden Menschen,’ Vienna, 1819; French edit., by Grundler, 1824.—Idem, ‘Icones helminthium,’ Vienna, 1824.—Cobbold, T. S., ‘Entozoa, an Introduction to the Study of Helminthology, with reference more particularly to the Parasites of Man,’ London, 1864; Supp., 1869.—Reviews in the ‘Lancet,’ Sept. 24th, 1864, p. 353; in the ‘Med. Times and Gaz.,’ Oct. 29th, 1864, p. 474; in the ‘AthenÆum,’ Oct. 15th, 1864, p. 493; in ‘Cosmos,’ Oct. 27th, 1864, p. 463; in the ‘Reader,’ Nov. 26th, 1864, p. 668; in the ‘Edinburgh Vet. Review,’ Nov., 1864, p. 662; in ‘Intellectual Observer,’ vol. vi, 1864, p. 190; in the ‘Quarterly Journal of Science,’ No. v, January, 1865, p. 145; in the ‘Quart. Journ. of Micr. Science,’ New Series, No. 17, Jan., 1865, p. 43; in ‘Popular Science Review,’ Jan., 1865, p. 214; in the ‘Veterinarian,’ Feb., 1865, p. 97; in the ‘Medical Mirror,’ Jan., 1865, p. 23; in the ‘Natural History Review’ for July, 1865; in the ‘British and Foreign Medico-Chirurgical Review,’ April, 1865, in the ‘Edinburgh Medical Journal’ for April, p. 929; in the ‘Social Science Review’ for Feb. 1, 1866, p. 169; in ‘Dublin Quart. Journ. of Medical Science’ for Aug., 1867.—Davaine, C., ‘TraitÉ des Entozoaires et des maladies vermineuses de l’homme et des animaux domestiques,’ Paris, 1860, 2nd edit., 1877–79.—Diesing, C. M., ‘Systema helminthum,’ Vienna, 1850.—Dujardin, F., ‘Histoire naturelle des helminthes ou vers intestineaux,’ Paris, 1845.—Goeze, T. A. S., ‘Versuch einer Naturgeschichte der EingeweidewÜrmer thierischer KÖrper,’ Blankenburgh, 1782.—KÜchenmeister, F., ‘Die in und an dem KÖrper des lebenden Menschen vorkommenden Parasiten,’ Leipsic, 1855, 2nd. edit., 1878–79; Eng. edit., by Lankester, 1857.—Le Clerc, D., ‘A Natural and medicinal History of Worms bred in the bodies of men and other animals’ (sic), Browne’s edit., London, 1721.—Leuckart, R., ‘Die menschlichen Parasiten, und die von ihren herruhrenden Krankheiten,’ Leipsic und Heidelberg, 1863–1876.—Redi, F., ‘De animalculis vivis quÆ in corporibus animalium vivorum reperiuntur, observationes;’ Coste’s edition, AmstelÆdami, 1688.—Rudolphi, C. A., ‘Entozoorum sive vermium intestinalium historia naturalis,’ Amsterdam, 1808.—Idem, ‘Entozoorum Synopsis,’ Berlin, 1819.—Van Beneden, P. J., ‘Animal Parasites and Messmates,’ London, 1876.

Several of the above works, while professing to deal with human parasites only, cover more or less of the whole ground of helminthology. Leuckart’s work is invaluable in this respect; and in the matter of literary references of a professional kind Davaine’s treatise is itself well nigh exhaustive. In any ordinary volume it is not possible to give a complete bibliography of parasitism. I make no pretension to do so here; nevertheless, the large number of modern memoirs that I have received from the distinguished writers themselves, enables me to render this part of my book very useful. As second only in importance to the above-mentioned works may be added the following—whether minor treatises, memoirs, monographs, comprehensive articles, or reports of a general or special character, respectively. As such it will be seen that some of them are sufficiently comprehensive, and their mere enumeration will enable the beginner to realise something like a fair estimate of the scope of helminthology. In the case of my own works I have ventured to add references to reviews and notices, because many of the latter contain valuable original suggestions made by the various anonymous writers.

Bibliography (No. 2).—Bastian, H. C., “On the Anatomy and Physiology of the Nematoids, parasitic and free,” ‘Philosophical Transactions,’ 1865 (see also Bibliog., No. 60).—Cobbold, T. S., ‘Worms; a series of lectures on Practical Helminthology,’ London, 1872; Italian edition by Tommasi. Milan, Florence, &c., 1873.—Idem, ‘The Internal Parasites of our Domesticated Animals,’ London, 1873; Italian edit. by Tommasi, Florence, 1874.—Idem, ‘Tapeworms (Human), their Sources, Varieties, and Treatment,’ London, 3rd edit., 1875. Reviews (1st and 2nd edit., with ‘Threadworms’), in ‘Brit. and For. Med.-Chir. Review’ for 1867, p. 433; in ‘Edin. Med. Journ.’ for 1866–67, p. 107; in ‘Lancet,’ Nov. 10th, 1866; in ‘Popular Science Review,’ Oct. 1st, 1866; in ‘Intellectual Observer,’ Oct. 1866; in ‘Med. Press and Circular,’ Jan. 16th, 1867; again in the ‘Lancet,’ for March 13th, 1867; and in ‘Dublin Quart. Journ. of Medical Science’ for 1867, 3rd edit.; in the ‘Field,’ Sept. 25th, 1875; and in ‘Popular Science Review’ for Jan., 1876.—Idem, ‘Catalogue of the Specimens of Entozoa in the Museum of the Royal College of Surgeons of England,’ London, 1866; noticed in the ‘Lancet’ for March 24th, 1866, p. 321.—Idem, “On the best Methods of displaying Entozoa in Museums,” ‘Journ. Linn. Soc.,’ vol. viii, p. 170.—Idem, ‘New Entozootic Malady,’ &c., 1864; popular brochure, reviewed in the ‘Lancet,’ Feb. 4th, 1865, p. 128; in the ‘AthenÆum,’ Jan. 21st, 1865, p. 87; in the ‘British Med. Journal,’ Jan., 1865; in the ‘Veterinary Review and Stockowners’ Journal,’ No. 2, New Series, Feb., 1865, p. 76; in the ‘Reader,’ Feb. 4th, 1865, p. 142; in ‘Med. Times and Gaz.’ for June 2nd, 1865; in the ‘Field’ for March 18th, 1865.—Idem, “Parasites of Man,” forming a series of articles contributed to the ‘Midland Naturalist,’ 1878–79.—Idem, “Notes on Entozoa contained in the various Metropolitan Museums,” in ‘Lancet,’ May 13th, 1865, p. 503.—Idem, “Report on Plica polonica, in reference to Parasites,” in ‘Pathological Soc. Trans.,’ 1866, p. 419.—Idem, “Report on Experiments respecting the Development and Migrations of the Entozoa,” ‘British Assoc. Reports’ (Bath Meeting) for 1864, p. 111; and briefly noticed in ‘Lancet’ for Sept. 24th, 1864.—Idem, Miscellaneous observations, including “Note on Parasites in the Lower Animals,” in ‘Dub. Med. Press’ for Feb. 11th, 1863, p. 154.—Idem, “Vegetables, Fruits, and Water considered as sources of Intestinal Worms;” in the ‘Popular Science Review’ for Jan., 1865, p. 163.—Idem (anonymously), “On Comparative Pathology and Therapeutics” (in relation to EntozoÖtics); leading art. in ‘Lancet’ for Dec. 9th, 1865, p. 652.—Idem, “List of Entozoa, including Pentastomes, from animals dying at the Zoological Society’s Menagerie, between 1857–60 inclusive, with descriptions of several new species,” ‘Proc. Zool. Soc.,’ 1861.—Idem, “Remarks on all the Human Entozoa,” ‘Proc. Zool. Soc.,’ 1862; abstracts in ‘Brit. Med. Journ.’ for 1862, and in ‘Edinb. New Phil. Journ.,’ vol. xvii, new series, 1863, p. 145; in Report of the ‘Proceed. of the Brit. Assoc. at Cambridge,’ 1862.—Idem, “Our Food-producing Ruminants, and the Parasites which reside in them; being the Cantor Lectures of the Society for the Encouragement of Arts, Manufactures, and Commerce,” delivered in 1871, and pub. in the ‘Journal of the Soc. of Arts’ for that year.—Davaine, C., “Les CestoÏdes,” in ‘Dict. Encycl. des Sci. Med.,’ Paris, 1876.—Eberth, C. J., ‘Untersuchungen ueber Nematoden,’ Leipsic, 1863.—Heller, A., “Darmschmarotzer,” in Von Ziemssen’s ‘Handbuch,’ Bd. vii, 1876; and in the American edition of the same, 1877.—Jones, T. R., “List of Entozoa of Greenland,” taken from Krabbe; ‘Arctic Manual,’ 1875, p. 179.—Krabbe, H., ‘Helminthologiske Undersogelser,’ Copenhagen, 1865.—Leuckart, R., ‘Die BlasenbandwÜrmer und ihre Entwicklung,’ Giessen, 1856.—Moquin-Tandon, A., “Epizoa and Entozoa,” in Hulme’s edit. of his ‘Elements of Medical Zoology,’ London, 1871.—Nordmann, A. von, ‘Mikrographische BeitrÄge zur Naturgeschichte der wirbellosen Thiere,’ Berlin, 1832.—Olsson, P., “Entozoa, iakttagna hos Skandanaviska hafsfiskar.,” Lund, ‘Univ. Årsskrift,’ 1867.—Owen, R., “Entozoa,” art. in Todd’s ‘CyclopÆdia of Anat. and Physiol.,’ London, 1839.—Idem, “Entozoa,” ‘Lectures (iv and v) on the Comp. Anat. and Physiol. of the Invertebrate Animals,’ London, 1855.—Pagenstecher, H. A., ‘Trematodenlarven und Trematoden,’ Heidelberg, 1857.—Rhind, W., ‘A Treatise on the Nature and Cure of Intestinal Worms, &c.,’ London, 1829.—Rolleston, G., “Characteristics of Nematelminthes and Platyelminthes,” in his ‘Forms of Animal Life,’ Oxford, 1870.—Schneider, A., ‘Monographie der Nematoden,’ Berlin, 1866.—Siebold, C. von., “Parasiten,” art. in Wagener’s ‘HandwÖrterbuch der Physiol., &c.,’ 1845.—Idem, “Helminthes,” Book v, in Burnett’s edit. of Siebold and Stannius’ ‘Comparative Anatomy,’ London and Boston, 1854.—Thomson, A., “Entozoa,” in the art. “Ovum,” in Todd’s ‘Cyclop. of Anat. and Physiol.,’ London, 1859.—Van Beneden, P. J., ‘MÉmoire sur les Vers Intestineaux,’ Paris, 1858.—Idem, “Les Vers CestoÏdes,” ‘MÉm. de l’Acad. Roy.,’ Brussels, 1850.—Verrill, A. E., “The External and Internal Parasites of Man and the Domestic Animals,” ‘Rep. of Board of Agriculture,’ Connecticut, U.S., 1870.—Von Baer, K. E., ‘Observations on Entozoa;’ in an analytical notice of his article “BeitrÄge zur Kentniss der niedern Thiere,” from ‘Nova Acta Nat. Cur.,’ tom. xiii, in the ‘Zool. Journ.,’ vol. iv, p. 250, 1828–29.—Wagener, G. R., ‘BeitrÄge zur Entwicklungsgeschichte der EingeweidewÜrmer,’ Haarlem, 1857.—Weinland, D. F., ‘An Essay on the Tapeworms of Man,’ Cambridge, U.S., 1858.