EMBRYOLOGY.

PART II. ORGANOGENY.

OF

FRANCIS MAITLAND BALFOUR.

VOL. III.

Memorial Edition.

Cambridge:
PRINTED BY C. J. CLAY, M.A. AND SON,
AT THE UNIVERSITY PRESS.

Memorial Edition.

THE WORKS
OF
FRANCIS MAITLAND BALFOUR,

M.A., LL.D., F.R.S.,

FELLOW OF TRINITY COLLEGE,
AND PROFESSOR OF ANIMAL MORPHOLOGY IN THE UNIVERSITY OF
CAMBRIDGE.

EDITED BY

M. FOSTER, F.R.S.,
PROFESSOR OF PHYSIOLOGY IN THE UNIVERSITY OF CAMBRIDGE;

AND

ADAM SEDGWICK, M.A.,
FELLOW AND LECTURER OF TRINITY COLLEGE, CAMBRIDGE.

VOL. III.

A TREATISE ON COMPARATIVE EMBRYOLOGY.

Vol. II. Vertebrata.

London:
MACMILLAN AND CO.
1885

[The Right of Translation is reserved.]

PREFACE TO VOLUME II.

The present volume completes my treatise on Comparative Embryology. The first eleven chapters deal with the developmental history of the Chordata. These are followed by three comparative chapters completing the section of the work devoted to Systematic Embryology. The remainder of the treatise, from Chapter XIV. onwards, is devoted to Organogeny. For the reasons stated in the introduction to this part the organogeny of the Chordata has been treated with much greater fulness than that of the other groups of Metazoa.

My own investigations have covered the ground of the present volume much more completely than they did that of the first volume; a not inconsiderable proportion of the facts recorded having been directly verified by me.

The very great labour of completing this volume has been much lightened by the assistance I have received from my friends and pupils. Had it not been for their co-operation a large number of the disputed points, which I have been able to investigate during the preparation of the work, must have been left untouched.

My special thanks are due to Mr Sedgwick, who has not only devoted a very large amount of time and labour to correcting the proofs, but has made for me an index of this volume, and has assisted me in many other ways.

Dr Allen Thomson and Professor Kleinenberg of Messina have undertaken the ungrateful task of looking through my proof-sheets, and have made suggestions which have proved most valuable. To Professors Parker, Turner, and Bridge, I am also greatly indebted for their suggestions with reference to special chapters of the work.

CONTENTS OF VOLUME II.

Chapter I. Cephalochorda. Pp. 1-8.

Segmentation and formation of the layers, pp. 1-3. Central nervous system, pp. 3, 4. Mesoblast, p. 5. General history of larva, pp. 6-8.

Chapter II. Urochorda. Pp. 9-39.

Solitaria, pp. 9-23. Development of embryo, pp. 9-15. Growth and structure of free larva, pp. 15-19. Retrogressive metamorphosis, pp. 19-23. Sedentaria, p. 23. Natantia, pp. 23-28. DoliolidÆ, pp. 28, 29. SalpidÆ, pp. 29-34. Appendicularia, p. 34. Metagenesis, pp. 34-38.

Chapter III. Elasmobranchii. Pp. 40-67.

Segmentation and formation of the layers, pp. 40-47. Epiblast, p. 47. Mesoblast, pp. 47-51. Hypoblast and notochord, pp. 51-54. General features of the embryo at successive stages, pp. 55-62. The yolk-sack, pp. 62-66.

Chapter IV. Teleostei. Pp. 68-82.

Segmentation and formation of the layers, pp. 68-73. General history of the layers, pp. 73-75. General development of the embryo, pp. 76-81.

Chapter V. Cyclostomata. Pp. 83-101.

Segmentation and formation of the layers, pp. 83-86. Mesoblast and notochord, pp. 86, 87. General history of the development, pp. 87-97. Metamorphosis, pp. 97-100. Myxine, p. 100.

Chapter VI. Ganoidei. Pp. 102-119.

Acipenser, pp. 102-110. Segmentation and formation of the layers, pp. 102-104. General development of the embryo and larva, pp. 104-110. Lepidosteus, pp. 111-119. Segmentation, pp. 111, 112. General development of embryo and larva, pp. 112-119. General observations on the embryology of Ganoids, p. 119.

Chapter VII. Amphibia. Pp. 120-144.

Oviposition and impregnation, pp. 120, 121. Formation of the layers, pp. 121-124. Epiblast, pp. 125-127. Mesoblast and notochord, pp. 128, 129. Hypoblast, pp. 129-131. General growth of the embryo, pp. 131-143. Anura, pp. 131-141. Urodela, pp. 141-143. Gymnophiona, p. 143.

Chapter VIII. Aves. Pp. 145-201.

Segmentation and formation of the layers, pp. 145-166. General history of of the germinal layers, pp. 166-169. General development of the embryo, pp. 169-180. Foetal membranes, pp. 185-199. Amnion, pp. 185-191. Allantois, pp. 191-193. Yolk-sack, pp. 193-199.

Chapter IX. Reptilia. Pp. 202-213.

Lacertilia, pp. 202-209. Segmentation and formation of the layers, pp. 202-207. General development of the embryo, p. 208. Embryonic membranes and yolk-sack, pp. 208-210. Ophidia, p. 210. Chelonia, pp. 210-212.

Chapter X. Mammalia. Pp. 214-274.

Segmentation and formation of the layers, pp. 214-227. General growth of the embryo, pp. 227-232. Embryonic membranes and yolk-sack, pp. 232-239. Comparative history of the Mammalian foetal membranes, pp. 239-257. Comparative histology of the placenta, pp. 257-259. Evolution of the placenta, pp. 259-261. Development of the Guinea-pig, pp. 262-265. The human embryo, pp. 265-270.

Chapter XI. Comparison of the formation of the Germinal Layers and of the early stages in the development of Vertebrates. Pp. 275-310.

Formation of the gastrula, pp. 275-292. The formation of the mesoblast and of the notochord, pp. 292-300. The epiblast, pp. 300-304. Formation of the central nervous system, pp. 301-304. Formation of the organs of special sense, p. 304. Summary of organs derived from the three germinal layers, pp. 304-306. Growth in length of the Vertebrate embryo, pp. 306-309. The evolution of the allantois and amnion, pp. 309, 310.

Chapter XII. Observations on the ancestral form of the Chordata. Pp. 311-330.

General considerations, pp. 311-316. The medullary canal, pp. 316, 317. The origin and nature of the mouth, pp. 317-321. The cranial flexure, pp. 321, 322. The postanal gut and neurenteric canal, pp. 322-325. The body-cavity and mesoblastic somites, p. 325. The notochord, pp. 325, 326. Gill clefts, pp. 326, 327. Phylogeny of the Chordata, pp. 327-329.

Chapter XIII. General Conclusions. Pp. 331-388.

I. Mode of origin and homologies of the germinal layers, pp. 331-360. Formation of the primary germinal layers, pp. 332, 333. Invagination, pp. 333-335. Delamination, pp. 335-338. Phylogenetic significance of delamination and invagination, pp. 338-345. Homologies of the germinal layers, pp. 345, 346. The origin of the mesoblast, pp. 346-360.

II. Larval forms: their nature, origin, and affinities. Preliminary considerations, pp. 360-362. Types of larvÆ, pp. 363-384. Phylogenetic conclusions, pp. 384, 385. General conclusions and summary, pp. 385, 386.

PART II. ORGANOGENY;

Introduction. Pp. 391, 392.

Chapter XIV. The Epidermis and its Derivatives. Pp. 393-399.

Protective epidermic structures, pp. 393-397. Dermal skeletal structures, p. 397. Glands, pp. 397, 398.

Chapter XV. The Nervous System. Pp. 400-469.

The origin of the nervous system, pp. 400-405. Nervous system of the Invertebrata, pp. 405-414. Central nervous system of the Vertebrata, pp. 415-447. Spinal chord, pp. 415-419. General development of the brain, pp. 419-423. Hind-brain, pp. 424-427. Mid-brain, pp. 427, 428. General development of fore-brain, pp. 428-430. Thalamencephalon, pp. 430-435. Pituitary body, pp. 435-437. Cerebral Hemispheres, pp. 437-444. Olfactory lobes, pp. 444, 445. General conclusions as to the central nervous system of the Vertebrata, pp. 445-447. Development of the cranial and spinal nerves, pp. 448-466. Spinal nerves, pp. 448-455. Cranial nerves, pp. 455-466. Sympathetic nervous system, pp. 466-468.

Chapter XVI. Organs of Vision. Pp. 470-511.

Coelenterata, pp. 471, 472. Mollusca, pp. 472-479. ChÆtopoda, p. 479. ChÆtognatha, p. 479. Arthropoda, pp. 479-483. Vertebrata general, pp. 483-490. Retina, pp. 490-492. Optic nerve, pp. 492, 493. Choroid fissure, p. 493. Lens, pp. 494, 495. Vitreous humour, pp. 494, 495. Cornea, pp. 495-497. Aqueous humour, p. 497. Comparative development of Vertebrate eye, pp. 497-506. Ammocoete eye, pp. 498, 499. Optic vesicles, p. 499. Lens, p. 499. Cornea, p. 500. Optic nerve and choroid fissure, pp. 500-505. Iris and ciliary processes, p. 506. Accessory organs connected with the eye, p. 506. Eyelids, p. 506. Lacrymal glands, p. 506. Lacrymal duct, pp. 506, 507. Eye of the Tunicata, pp. 507-509. Accessory eyes in the Vertebrata, pp. 509, 510.

Chapter XVII. Auditory organ, Olfactory organ, and Sense organs of the Lateral line. Pp. 512-541.

Auditory organs, pp. 512-531. General structure of auditory organs, pp. 512, 513. Auditory organs of the Coelenterata, pp. 513-515. Auditory organs of the Mollusca, pp. 515, 516. Auditory organs of the Crustacea, p. 516. Auditory organs of the Vertebrata, pp. 516-530. Auditory vesicle, pp. 517-524. Organ of Corti, pp. 524-527. Accessory structures connected with the organ of hearing of terrestrial vertebrata, pp. 527-530. Auditory organ of the Tunicata, pp. 530, 531. Bibliography of Auditory organs, p. 531.

Olfactory organs, pp. 531-538. Bibliography of Olfactory organs, p. 538. Sense organs of the lateral line, pp. 538-540. Bibliography of sense organs of lateral line, pp. 540, 541.

Chapter XVIII. The Notochord, the Vertebral Column, the Ribs, and the Sternum. Pp. 542-563.

Introductory remarks on the origin of the skeleton, pp. 542-544. Bibliography of the origin of the skeleton, pp. 544, 545. The notochord and its cartilaginous sheath, pp. 545-549. The vertebral arches and the vertebral bodies, pp. 549-559. Cyclostomata, p. 549. Elasmobranchii, pp. 549-553. Ganoidei, p. 553. Teleostei, p. 553. Amphibia, pp. 553-556. Reptilia, pp. 556, 557. Aves, pp. 557, 558. Mammalia, pp. 558, 559. Bibliography of the notochord and vertebral column, p. 560. Ribs, pp. 560-562. Sternum, pp. 562, 563. Bibliography of the ribs and sternum, p. 563.

Chapter XIX. The Skull. Pp. 564-598.

Preliminary remarks, pp. 564, 565. The cartilaginous cranium, pp. 565-571. The parachordals and notochord, pp. 566, 567. The trabeculÆ, pp. 567-570. The sense capsules, pp. 570, 571. The branchial skeleton, pp. 572-591. General structure of, pp. 572-575. Mandibular and hyoid arches, pp. 575-591. Elasmobranchii, pp. 576-579. Teleostei, pp. 579-581. Amphibia, pp. 581-588. Sauropsida, pp. 588, 589. Mammalia, pp. 589-591. Membrane bones and ossifications of the cranium, pp. 592-597. Membrane bones, pp. 592-595. Ossifications of the cartilaginous cranium, pp. 595-597. Labial cartilages, p. 597. Bibliography of the skull, p. 598.

Chapter XX. Pectoral and Pelvic Girdles and the Skeleton of the Limbs. Pp. 599-622.

The Pectoral girdle, pp. 599-606. Pisces, pp. 599-601. Amphibia and Amniota, pp. 601, 602. Lacertilia, p. 603. Chelonia, p. 603. Aves, pp. 603, 604. Mammalia, p. 604. Amphibia, p. 605. Bibliography of Pectoral girdle, pp. 605, 606.

The Pelvic girdle, pp. 606-608. Pisces, pp. 606, 607. Amphibia and Amniota, pp. 606, 607. Amphibia, p. 607. Lacertilia, p. 607. Mammalia, p. 608. Bibliography of Pelvic girdle, p. 608. Comparison of pectoral and pelvic girdles, pp. 608, 609.

Limbs, pp. 609-622. The piscine fin, pp. 609-618. The cheiropterygium, pp. 618-622. Bibliography of limbs, p. 622.

Chapter XXI. The Body Cavity, the Vascular System and the Vascular Glands. Pp. 623-666.

The body cavity, pp. 623-632. General, pp. 623, 624. Chordata, pp. 624-632. Abdominal pores, pp. 626, 627. Pericardial cavities, pleural cavities and diaphragm, pp. 627-632. Bibliography of body cavity, p. 632.

The vascular system, pp. 632-663. General, pp. 632, 633. The heart, pp. 633-643. Bibliography of the heart, p. 643. Arterial system, pp. 643-651. Bibliography of the arterial system, p. 651. Venous system, pp. 651-663. Bibliography of the venous system, p. 663. Lymphatic system and spleen, p. 664. Bibliography of spleen, p. 664. Suprarenal bodies, pp. 664-666. Bibliography of suprarenal bodies, p. 666.

Chapter XXII. The Muscular System. Pp. 667-679.

Evolution of muscle-cells, pp. 667, 668. Voluntary muscular system of the Chordata, pp. 668-679. Muscular fibres, pp. 668, 669. Muscular system of the trunk and limbs, pp. 673-676. The somites and muscular system of the head, pp. 676-679. Bibliography of muscular system, p. 679.

Chapter XXIII. Excretory organs. Pp. 680-740.

Platyelminthes, pp. 680, 681. Mollusca, pp. 681, 682. Polyzoa, pp. 682, 683. Branchiopoda, p. 683. ChÆtopoda, pp. 683-686. Gephyrea, pp. 686, 687. Discophora, pp. 687, 688. Arthropoda, pp. 688, 689. Nematoda, p. 689. Excretory organs and generative ducts of the Craniata, pp. 689-737. General, pp. 689, 690. Elasmobranchii, pp. 690-699. Cyclostomata, pp. 700, 701. Teleostei, pp. 701-704. Ganoidei, pp. 704-707. Dipnoi, p. 707. Amphibia, pp. 707-713. Amniota, pp. 713-727. General conclusions and summary, pp. 728-737. Pronephros, pp. 728, 729. Mesonephros, pp. 729-732. Genital ducts, pp. 732-736. Metanephros, pp. 736, 737. Comparison of the excretory organs of the Chordata and Invertebrata, pp. 737, 738. Bibliography of Excretory organs, pp. 738-740.

Chapter XXIV. Generative Organs and Genital Ducts. Pp. 741-753.

Generative organs, pp. 741-748. Porifera, p. 741. Coelenterata, pp. 741-743. ChÆtopoda and Gephyrea, p. 743. ChÆtognatha, pp. 743-745. Polyzoa, p. 745 Nematoda, p. 745. Insecta, p. 745. Crustacea, pp. 745, 746. Chordata, pp. 746-748. Bibliography of generative organs, p. 748. Genital ducts, pp. 748-753.

Chapter XXV. The Alimentary Canal and its appendages in the Chordata. Pp. 754-780.

Mesenteron, pp. 754-774. Subnotochordal rod, pp. 754-756. Splanchnic mesoblast and mesentery, pp. 756-758. Respiratory division of the Mesenteron, pp. 758-766. Thyroid body, pp. 759-762. Thymus gland, pp. 762, 763. Swimming bladder and lungs, pp. 763-766, The middle division of the Mesenteron, pp. 766-771. Cloaca, pp. 766, 767. Intestine, pp. 767, 768. Liver, pp. 769, 770. Pancreas, pp. 770, 771. Postanal section of the Mesenteron, pp. 771-774.

The stomodÆum, pp. 774-778. Comparative development of oral cavity, pp. 774-776. Teeth, pp. 776-778.

The proctodÆum, pp. 778-780. Bibliography of alimentary canal, p. 780.