Chapter XXV (2)

In the next stage a cap of dentine has become formed, while in the still older tooth this has become covered by a layer of enamel. As may be gathered from this diagram, the primitive epithelial ridge from which the enamel organ is formed is not necessarily absorbed on the formation of a tooth, but is capable of giving rise to fresh enamel organs. When the enamel organ has reached a certain stage of development, its connection with the epithelial ridge is ruptured (fig. 428).

The arrangement represented in fig. 428, in which successive enamel organs are formed from the same epithelial ridge, is found in most Vertebrata except the Teleostei. In the Teleostei, however (Tomes), a fresh enamel organ grows inwards from the epithelium for each successively formed tooth.

_The Proctodæum._

In all Vertebrata the cloacal section of the alimentary tract which receives the urinogenital ducts is placed in communication with the exterior by means of an epiblastic invagination, constituting a proctodæum.

This invagination is not usually very deep, and in most instances the boundary wall between it and the hypoblastic cloaca is not perforated till considerably after the perforation of the stomodæum; in Petromyzon, however, its perforation is effected before the mouth and pharynx are placed in communication.

The mode of formation of the proctodæum, which is in general extremely simple, is illustrated by fig. 420 _an_.

In most forms the original boundary between the epiblast of the proctodæum and the hypoblast of the primitive cloaca becomes obliterated after the two have become placed in free communication.

[FIG. 429. DIAGRAMMATIC LONGITUDINAL SECTION THROUGH THE POSTERIOR
END OF AN EMBRYO BIRD AT THE TIME OF THE FORMATION OF THE ALLANTOIS.

_ep._ epiblast; _Sp.c._ spinal canal; _ch._ notochord; _n.e._
neurenteric canal; _hy._ hypoblast; _p.a.g._ postanal gut; _pr._
remains of primitive streak folded in on the ventral side; _al._
allantois; _me._ mesoblast; _an._ point where anus will be formed;
_p.c._ perivisceral cavity; _am._ amnion; _so._ somatopleure; _sp._
splanchnopleure.]

In Birds the formation of the proctodæum is somewhat more complicated than in other types, owing to the outgrowth from it of the bursa Fabricii.

The proctodæum first appears when the folding off of the tail end of the embryo commences (fig. 429, _an_) and is placed near the front (originally the apparent hind) end of the primitive streak. Its position marks out the front border of the postanal section of the gut.

The bursa Fabricii first appears on the seventh day (in the chick), as a dorsal outgrowth of the proctodæum. The actual perforation of the septum between the proctodæum and the cloacal section of the alimentary tract is not effected till about the fifteenth day of foetal life, and the approximation of the epithelial layers of the two organs, preparatory to their absorption, is partly effected by the tunneling of the mesoblastic tissue between them by numerous spaces.

The hypoblastic section of the cloaca of birds, which receives the openings of the urinogenital ducts, is permanently marked off by a fold from the epiblastic section or true proctodæum, with which the bursa Fabricii communicates.

BIBLIOGRAPHY.

_Alimentary Canal and its appendages._

(561) B. Afanassiew. "Ueber Bau u. Entwicklung d. Thymus d. Säugeth." _Archiv f. mikr. Anat._ Bd. XIV. 1877.

(562) Fr. Boll. _Das Princip d. Wachsthums._ Berlin, 1876.

(563) E. Gasser. "Die Entstehung d. Cloakenöffnung bei Hühnerembryonen." _Archiv f. Anat. u. Physiol., Anat. Abth._ 1880.

(564) A. Götte. _Beiträge zur Entwicklungsgeschichte d. Darmkanals im Hühnchen._ 1867.

(565) W. Müller. "Ueber die Entwickelung der Schilddrüse." _Jenaische Zeitschrift_, Vol. VI. 1871.

(566) W. Müller. "Die Hypobranchialrinne d. Tunicaten." _Jenaische Zeitschrift_, Vol. VII. 1872.

(567) S. L. Schenk. "Die Bauchspeicheldrüse d. Embryo." _Anatomischphysiologische Untersuchungen._ 1872.

(568) E. Selenka. "Beitrag zur Entwicklungsgeschichte d. Luftsäcke d. Huhns." _Zeit. f. wiss. Zool._ 1866.

(569) L. Stieda. _Untersuch. üb. d. Entwick. d. Glandula Thymus, Glandula thyroidea, u. Glandula carotica._ Leipzig, 1881.

(570) C. Fr. Wolff. "De formatione intestinorum." _Nov. Comment. Akad. Petrop._ 1766.

(571) H. Wölfler. _Ueb. d. Entwick. u. d. Bau d. Schilddrüse._ Berlin, 1880.

_Vide_ also Kölliker (298), Götte (296), His (232 and 297), Foster and Balfour (295), Balfour (292), Remak (302), Schenk (303), etc.

_Teeth._

(572) T. H. Huxley. "On the enamel and dentine of teeth." _Quart. J. of Micros. Science_, Vol. III. 1855.

(573) R. Owen. _Odontography._ London, 1840-1845.

(574) Ch. S. Tomes. _Manual of dental anatomy, human and comparative._ London, 1876.

(575) Ch. S. Tomes. "On the development of teeth." _Quart. J. of Micros. Science_, Vol. XVI. 1876.

(576) W. Waldeyer. "Structure and development of teeth." _Stricker's Histology._ 1870.

_Vide_ also Kölliker (298), Gegenbaur (294), Hertwig (306), etc.

INDEX TO VOLUME III.

Abdominal muscles, 675

Abdominal pore, 626, 749

Acipenser, development of, 102;
affinities of, 118;
comparison of gastrula of, 279;
pericardial cavity of, 627

Actinotrocha, 373

Air-bladder of Teleostei, 77;
Lepidosteus, 117;
blood supply of, 645;
general account of, 763;
homologies of, 766

Alciope, eye of, 480

Alisphenoid region of skull, 569

Alimentary canal and appendages, development of, 754

Alimentary tract of Ascidia, 18;
Molgula, 22;
Pyrosoma, 24;
Salpa, 31;
Elasmobranchii, 52;
Teleostei, 75;
Petromyzon, 93, 97;
Acipenser, 110;
Amphibia, 129, 136;
Chick, 167;
respiratory region of, 754;
temporary closure of oesophageal region of, 759

Allantois, development of in Chick, 191, 198;
blood-vessels of in Chick, 193;
Lacerta, 205, 209;
early development of in Rabbit, 229;
of Guinea-pig, 264;
origin of, 309.
_See also_ 'Placenta' and 'Bladder'

Alternation of generations in Ascidians, origin of, 35;
in Botryllus, 35;
Pyrosoma, 36;
Salpa, 36;
Doliolum, 36

Alytes, branchial chamber of, 136;
yolk-sack of, 139;
branchiæ, 141;
Müllerian duct of, 710

Amblystoma, ovum of, 120;
larva of, 142, 143

Amia, ribs of, 561

Ammocoetes, 95;
metamorphosis of, 97;
eye of, 498

Amnion, early development of in Chick, 185;
later history of in Chick, 196;
Lacerta, 204, 210;
Rabbit, 229;
origin of, 307, 309

Amphibia, development of, 120;
viviparous, 121;
gastrula of, 277;
suctorial mouth of, 317;
cerebellum of, 426;
infundibulum of, 431;
pineal gland of, 433;
cerebrum of, 439;
olfactory lobes of, 444;
nares of, 553;
notochord and its sheath, 548;
vertebral column of, 554;
ribs of, 561;
branchial arches of, 574;
mandibular and hyoid arches of, 582;
columella of, 582;
pectoral girdle of, 605;
pelvic girdle of, 607;
limbs of, 619;
heart of, 638;
arterial system of, 645;
venous system of, 655;
excretory system of, 707;
vasa efferentia of, 711;
liver of, 769;
postanal gut of, 774;
stomodæum of, 778

Amphiblastula larva of Porifera, 344

Amphioxus, development of, 1;
gastrula of, 275;
formation of mesoblast of, 292;
development of notochord of, 293;
head of, 314;
spinal nerves of, 461;
olfactory organ of, 462;
venous system of, 651;
transverse abdominal muscle of, 673;
generative cells of, 748;
liver of, 769;
postanal gut of, 772;
stomodæum of, 777

Amphistylic skulls, 578

Angular bone, 594

Anterior abdominal vein, 653

Anura, development of, 121;
epiblast of, 125;
mesoblast of, 128;
notochord of, 128;
hypoblast of, 129;
general growth of embryo of, 131;
larva of, 134;
vertebral column of, 556;
mandibular arch of, 584

Anus of Amphioxus, 7;
Ascidia, 18;
Pyrosoma, 28;
Salpa, 31;
Elasmobranchii, 57;
Amphibia, 130, 132;
Chick, 167;
primitive, 324

Appendicularia, development of, 34

Aqueductus vestibuli, 519

Aqueous humour, 497

Arachnida, nervous system of, 409;
eye of, 481

Area, embryonic, of Rabbit, 218;
epiblast of, 219;
origin of embryo from, 228;
area opaca of Chick, 150;
epiblast, hypoblast, and mesoblast of, 159;
area pellucida of Chick, 150;
of Lacerta, 202 area vasculosa of Chick, 194;
mesoblast of, 160;
of Lizard, 209;
Rabbit, 228, 229

Arteria centralis retinæ, 503

Arterial system of Petromyzon, 97;
constitution of in embryo, 643;
of Fishes, 644;
of Amphibia, 645;
of Amniota, 647

Arthropoda, head of, 313;
nervous system of, 409;
eye of, 480;
excretory organs of, 688

Articular bone of Teleostei, 581;
of Sauropsida, 588

Ascidia, development of, 9

Ascidians. _See_ 'Tunicata'

Ascidiozooids, 25

Atrial cavity of Amphioxus, 7;
Ascidia, 18;
Pyrosoma, 24

Atrial pore of Amphioxus, 7;
Ascidia, 20;
Pyrosoma, 28;
Salpa, 32

Auditory capsules, ossifications in, 595, 596

Auditory involution of Elasmobranchii, 57;
Teleostei, 73;
Petromyzon, 89, 92;
Acipenser, 106;
Lepidosteus, 114;
Amphibia, 127;
Chick, 170

Auditory nerve, development of, 459

Auditory organs, of Ascidia, 15;
of Salpa, 31;
of Ammocoetes, 98;
Ganoidei, 108, 114;
of Amphibia, 127;
of Aves, 170;
general development of, 512;
of aquatic forms, 512;
of land forms, 513;
of Coelenterata, 513;
of Mollusca, 515;
of Crustacea, 516;
of Vertebrata, 517;
of Cyclostomata, 89, 92, 518;
of Teleostei, Lepidosteus and Amphibia, 518;
of Mammalia, 519;
accessory structures of, 527;
of Tunicata, 528

Auriculo-ventricular valves, 642

Autostylic skulls, 579

Aves, development of, 145;
cerebellum of, 426;
mid-brain of, 427;
infundibulum of, 431;
pineal gland of, 434;
pituitary body of, 436;
cerebrum of, 439;
olfactory lobes of, 444;
spinal nerves of, 449;
cranial nerves of, 455;
vagus of, 458;
glossopharyngeal of, 458;
vertebral column of, 557;
ossification of vertebral column of, 558;
branchial arches of, 572, 573;
pectoral girdle of, 603;
pelvic girdle of, 608;
heart of, 637;
arterial system of, 647;
venous system of, 658;
muscle-plates of, 670;
excretory organs of, 714;
mesonephros of, 715;
pronephros of, 718;
Müllerian duct of, 718, 720;
nature of pronephros of, 721;
connection of Müllerian duct with Wolffian in, 720;
kidney of, 722;
lungs of, 764;
liver of, 769;
postanal gut of, 774

Axolotl, 142, 143;
ovum of, 120;
mid-brain of, 427;
mandibular arch of, 583

Basilar membrane, 524

Basilar plate, 565

Basipterygium, 612

Basisphenoid region of skull, 569

Bilateral symmetry, origin of, 373-376

Bile duct, 770

Bladder, Amphibia, 131;
of Amniota, 726

Blastodermic vesicle, of Rabbit, first development of, 217;
of 7th day, 222;
Guinea-pig, 263;
meaning of, 291

Blastoderm of Pyrosoma, 24;
Elasmobranchii, 41;
Chick, 150;
Lacerta 202

Blastopore, of Amphioxus, 2;
of Ascidia, 11;
Elasmobranchii, 42, 54, 62;
Petromyzon, 87;
Acipenser, 104;
Amphibia, 125, 130;
Chick, 153;
Rabbit, 216;
true Mammalian, 226;
comparative history of closure of, 284, 288;
summary of fate of, 340;
relation of to primitive anus, 324

Blood-vessels, development of, 633

Body cavity, of Ascidia, 21;
Molgula, 21;
Salpa, 31;
Elasmobranchii, 47;
of Teleostei, 75;
Petromyzon, 94;
Chick, 169;
development of in Chordata, 325;
views on origin of, 356-360, 377;
of Invertebrata, 623;
of Chordata, 624;
of head, 676

Bombinator, branchial chamber of, 136;
vertebral column of, 556

Bonellia, excretory organs of, 687

Bones, origin of cartilage bones, 542;
origin of membrane bones, 543;
development of, 543;
homologies of membrane bones, 542;
homologies of cartilage bones, 545

Brachiopoda, excretory organs of, 683;
generative ducts of, 749

Brain, of Ascidia, 11, 15;
Elasmobranchii, 56, 59, 60;
Teleostei, 77;
Petromyzon, 89, 92;
Acipenser, 105;
Lepidosteus, 113;
early development of in Chick, 170;
flexure of in Chick, 175;
later development of in Chick, 176;
Rabbit, 229;
general account of development of, 419;
flexure of, 420;
histogeny of, 422

Branchial arches, præoral, 570;
disappearance of posterior, 573;
dental plates of in Teleostei, 574;
relation of to head cavities, 571;
_see_ 'Visceral arches'

Branchial chamber of Amphibia, 136

Branchial clefts, of Amphioxus, 7;
of Ascidia, 18, 20;
Molgula, 23;
Salpa, 32;
of Elasmobranchii, 57, 59-61;
Teleostei, 77;
Petromyzon, 91, 96;
Acipenser, 105;
Lepidosteus, 114, 116;
Amphibia, 132, 133;
Chick, 178;
Rabbit, 231;
præoral, 312, 318;
of Invertebrata, 326;
origin of, 326

Branchial rays, 574

Branchial skeleton, development of, 572, 592;
of Petromyzon, 96, 312, 571;
of Ichthyopsida, 572;
dental plates of in Teleostei, 574;
relation of to head cavities, 572

Branchiæ, external of Elasmobranchii, 61, 62;
of Teleostei, 77;
Acipenser, 107;
Amphibia, 127, 133, 135

Brood-pouch, of Salpa, 29;
Teleostei, 68;
Amphibia, 121

Brown tubes of Gephyrea, 686

Bulbus arteriosus, of Fishes, 638;
Amphibia, 639

Bursa Fabricii, 167, 779

Canalis auricularis, 639

Canalis reuniens, 521

Capitellidæ, excretory organs of, 683

Carcharias, placenta of, 66

Cardinal vein, 652

Carnivora, placenta of, 250

Carpus, development of, 620

Cartilage bones of skull, 595;
homologies of, 595

Cat, placenta of, 250

Caudal swellings of Elasmobranchii, 46, 55;
Teleostei, 72;
Chick, 162, 170

Cephalic plate of Elasmobranchii, 55

Cephalochorda, development of, 1

Cephalopoda, eyes of, 473-477

Cerebellum, Petromyzon, 93;
Chick, 176;
general account of development of, 424, 425

Cerebrum of Petromyzon, 93, 97;
Chick, 175;
general development of, 429, 438;
transverse fissure of, 443

Cestoda, excretory organs of, 681

Cetacea, placenta, 255

Chætognatha, nervous system of, 349;
eye of, 479;
generative organs of, 743;
generative ducts of, 749

Chætopoda, head of, 313;
eyes of, 479;
excretory organs of, 683;
generative organs of, 743;
generative ducts of, 749

Charybdæa, eye of, 472

Cheiroptera, placenta of, 244

Cheiropterygium, 618;
relation of to ichthyopterygium, 621

Chelonia, development of, 210;
pectoral girdle of, 603;
arterial system of, 649

Chick, development of, 145;
general growth of embryo of, 170;
rotation of embryo of, 173;
foetal membranes of, 185;
epiblast of, 150, 166;
optic nerve and choroid fissure of, 500

Chilognatha, eye of, 481

Chilopoda, eye of, 481

Chimæra, lateral line of, 539;
vertebral column of, 548;
nares of, 533

Chiromantis, oviposition of, 121

Chorda tympani, development of, 460

Chordata, ancestor of, 311;
branchial system of, 312;
evidence from Ammocoetes, 312;
head of, 312;
mouth of, 318;
table of phylogeny of, 327

Chorion, 237;
villi of, 237, 257

Choroid coat, Ammocoetes, 99;
general account of, 487

Choroid fissure, of Vertebrate eye, 486, 493;
of Ammocoetes, 498;
comparative development of, 500;
of Chick, 501;
of Lizards, 501;
of Elasmobranchii, 502;
of Teleostei, 503;
Amphibia, 503;
Mammals, 503, 504

Choroid gland, 320

Choroid pigment, 489

Choroid plexus, of fourth ventricle, 425;
of third ventricle, 432;
of lateral ventricle, 442

Ciliated sack of Ascidia, 18;
Pyrosoma, 26;
Salpa, 31

Ciliary ganglion, 461

Ciliary muscle, 490

Ciliary processes, 488;
comparative development of, 506

Clavicle, 600

Clitoris, development of, 727

Clinoid ridge, 569

Cloaca, 766

Coccygeo-mesenteric vein, 661

Cochlear canal, 519

Coecilia, development of, 143;
pronephros of, 707;
mesonephros of, 709;
Müllerian duct of, 710

Coelenterata, larvæ of, 367;
eyes of, 471;
auditory organs of, 513;
generative organs of, 741

Columella auris, 529;
of Amphibia, 582;
of Sauropsida, 588

Commissures, of spinal cord, 417;
of brain, 431, 432, 439, 443

Coni vasculosi, 724

Conus arteriosus, of Fishes, 638;
of Amphibia, 638

Coracoid bone, 599

Cornea, of Ammocoetes, 99;
general development of, 495;
corpuscles of, 496;
comparative development of, 499;
of Mammals, 499

Coronoid bone, 595

Corpora geniculata interna, 428

Corpora quadrigemina, 428

Corpora striata, development of, 437

Corpus callosum, development of, 443

Corti, organ of, 522;
structure of, 525;
fibres of, 525;
development of, 526

Cranial flexure, of Elasmobranchii, 58, 60;
of Teleostei, 77;
Petromyzon, 93, 94;
of Amphibia, 131, 132;
Chick, 174;
Rabbit, 231;
characters of, 321;
significance of, 322

Cranial nerves, development of, 455;
relation of to head cavities, 461;
anterior roots of, 462-464;
view on position of roots of, 466

Crocodilia, arterial system of, 649

Crura cerebri, 429

Crustacea, nervous system of, 411;
eye of, 481;
auditory organs of, 515;
generative cells of, 745;
generative ducts of, 751

Cupola, 524

Cutaneous muscles, 676

Cyathozooid, 25

Cyclostomata, auditory organs of, 517;
olfactory organ of, 532;
notochord and vertebral column of, 546, 549;
abdominal pores of, 626;
segmental duct of, 700;
pronephros of, 700;
mesonephros of, 700;
generative ducts of, 733, 749;
venous system of, 651;
excretory organs of, 700

Cystignathus, oviposition of, 122

Dactylethra, branchial chamber of, 136;
branchiæ of, 136;
tadpole of, 140

Decidua reflexa, of Rat, 242;
of Insectivora, 243;
of Man, 245

Deiter's cells, 526

Dental papilla, 777

Dental capsule, 777

Dentary bone, 595

Dentine, 780

Descemet's membrane, 496

Diaphragm, 631;
muscle of, 676

Dipnoi, nares of, 534;
vertebral column of, 548;
membrane bones of skull of, 592;
heart of, 638;
arterial system of, 645;
excretory system of, 707;
stomodæum of, 777

Diptera, eye of, 481

Discophora, excretory organs of, 687

Dog, placenta of, 248

Dohrn, on relations of Cyclostomata, 84;
on ancestor of Chordata, 311, 319

Doliolum, development of, 28

Ductus arteriosus, 649

Ductus Botalli, 648

Ductus Cuvieri, 654

Ductus venosus Arantii, 663

Dugong, heart of, 642

Dysticus, eye of, 481

Ear, _see_ 'Auditory organ'

Echinodermata, secondary symmetry of larva of, 380;
excretory organs of, 689;
generative ducts of, 752

Echinorhinus, lateral line of, 539;
vertebral column of, 548

Echiurus, excretory organs of, 686

Ectostosis, 543

Edentata, placenta of, 248, 250, 256

Eel, generative ducts of, 703

Egg-shell of Elasmobranchii, 40;
Chick, 146

Elasmobranchii, development of, 40;
viviparous, 40;
general features of development of, 55;
gastrula of, 281;
development of mesoblast of, 294;
notochord of, 294;
meaning of formation of mesoblast of, 295;
restiform tracts of, 425;
optic lobes of, 427;
cerebellum of, 425;
pineal gland of, 432;
pituitary body of, 435;
cerebrum of, 438;
olfactory lobes of, 444;
spinal nerves, 449;
cranial nerves of, 457;
sympathetic nervous system of, 466;
nares of, 533;
lateral line of, 539;
vertebral column of, 549;
ribs of, 560;
parachordals of, 567;
mandibular and hyoid arches of, 576;
pectoral girdle of, 600;
pelvic girdle of, 607;
limbs of, 609;
pericardial cavity of, 627;
arterial system of, 644;
venous system of, 651;
muscle-plates of, 668;
excretory organs of, 690;
constitution of excretory organs in adult of, 697;
spermatozoa of, 747;
swimming-bladder of, 763;
intestines of, 767;
liver of, 769;
postanal gut of, 772

Elæoblast of Pyrosoma, 28;
Salpa, 30

Elephant, placenta of, 249

Embolic formation of gastrula, 333

Enamel organ, 777

Endolymph of ear, 522

Endostosis, 543

Endostyle of Ascidia, 18, 759;
Pyrosoma, 25;
Salpa, 32

Epiblast, of Elasmobranchii, 47;
Teleostei, 71, 75;
Petromyzon, 86;
Lepidosteus, 112;
Amphibia, 122, 125;
Chick, 149, 166;
Lacerta, 203;
Rabbit, 216, 219;
origin of in Rabbit, 221;
comparative account of development of, 300

Epibolic formation of gastrula, 334

Epichordal formation of vertebral column, 556

Epicrium glutinosum, 143

Epidermis, in Coelenterata, 393;
protective structures of, 394

Epididymis, 724

Epigastric vein, 653

Episkeletal muscles, 676

Episternum, 602

Epoophoron, 725

Ethmoid bone, 597

Ethmoid region of skull, 570

ethmo-palatine ligament of Elasmobranchs, 576

Euphausia, eye of, 483

Eustachian tube, of Amphibia, 135;
Chick, 180;
Rabbit, 232;
general development of, 528

Excretory organs, general constitution of, 680;
of Platyelminthes, 680;
of Mollusca, 681;
of Polyzoa, 682;
of Brachiopoda, 683;
of Chætopoda, 683;
of Gephyrea, 686;
of Discophora, 687;
of Arthropoda, 688;
of Nematoda, 689;
of Echinodermata, 689;
constitution of in Craniata, 689;
of Elasmobranchii, 690;
constitution of in adult Elasmobranch, 697;
of Petromyzon, 700;
of Myxine, 701;
of Teleostei,701;
of Ganoidei, 704;
of Dipnoi, 707;
of Amphibia, 707;
of Amniota, 713;
comparison of Vertebrate and Invertebrate, 737

Excretory system, of Elasmobranchii, 49;
Teleostei, 78;
Petromyzon, 95, 98;
Acipenser, 99;
Amphibia, 133

Exoccipital bone, 595

Exoskeleton, dermal, 393-395;
epidermal, 393-396

External generative organs, 726

Extra-branchial skeleton, 572

Eye, of Ascidia, 16;
Salpa, 31;
Elasmobranchii, 56, 57, 58;
Teleostei, 73;
Petromyzon, 92, 98;
Aves, 170;
Rabbit, 229;
general development of, 470;
evolution of, 470, 471;
simple, 480;
compound, 481;
aconous, 482;
pseudoconous, 482;
of Invertebrata, 471;
of Vertebrata, 483;
comparative development of Vertebrate, 497;
of Ammocoetes, 497;
of Tunicata, 507;
of Chordata, general views on, 508;
accessory eyes of Fishes, 509;
muscles of, 677

Eyelids, development of, 506

Falciform ligament, 757

Falx cerebri, 439

Fasciculi teretes, of Elasmobranchii, 426

Feathers, development of, 396

Fenestra rotunda and ovalis, 529

Fertilization, of Amphioxus, 2;
of Urochorda, 9;
Salpa, 29;
Elasmobranchii, 46;
of Teleostei, 68;
Petromyzon, 84;
Amphibia, 120;
Chick, 145;
Reptilia, 202;
meaning of, 331

Fifth nerve, development of, 460

Fifth ventricle, 443

Fins, of Elasmobranchii, 62;
Teleostei, 78;
Petromyzon, 94, 95;
Acipenser, 109;
Lepidosteus, 118;
relation of paired to unpaired, 611, 612;
development of pelvic, 614;
development of pectoral, 615;
views on nature of paired fins, 616

Fissures of spinal cord, 417

Foetal development, 360;
secondary variations in, 361

Foot, 618

Foramen of Munro, 430, 438

Foramen ovale, 642

Fore-brain, of Elasmobranchii, 55, 59, 60;
Petromyzon, 93;
general development of, 428

Formative cells, of Chick, 154

Fornix, development of, 443

Fornix of Gottsche, 428

Fourth nerve, 464

Frontals, 592

Frontonasal process of Chick, 179

Gaertner's canals, 724

Gall-bladder, 770

Ganoidei, development of, 102;
relations of, 118;
nares of, 534;
notochord of, 546;
vertebral column of, 546, 553;
ribs of, 561;
pelvic girdle of, 606;
arterial$ system of, 645;
excretory organs of, 704;
generative ducts of, 734

Gastropoda, eye of, 472

Gastrula, of Amphioxus, 2;
of Ascidia, 10;
Elasmobranchii, 43, 44;
Petromyzon, 86;
Acipenser, 103;
Amphibia, 123;
comparative development of, in Invertebrata, 275;
comparison of Mammalian, 291;
phylogenetic meaning of, 333;
ontogeny of (general), 333;
phylogeny of, 338-343;
secondary types of, 341

Geckos, vertebral column of, 557

Generative cells, development of, 741;
origin of in Coelenterata, 741;
of Invertebrata, 743;
of Vertebrata, 746

Generative ducts, of Teleostei, 704, 735;
of Ganoids, 704;
of Cyclostomata, 733;
origin of, 733;
of Lepidosteus, 735, 750;
development and evolution of, 748;
of Coelenterata, 748;
of Sagitta, 749;
of Tunicata, 749;
Chætopoda, Gephyrea, etc., 749;
of Mollusca, 751;
of Discophora, 751;
of Echinodermata, 752

Generative system of Elasmobranchii, 51

Gephyrea, nervous system of, 412;
excretory organs of, 686;
generative cells of, 743;
generative ducts of, 749

Germinal disc, of Elasmobranchii, 40;
Teleostei, 68;
Chick, 147

Germinal epithelium, 746

Germinal layers, summary of organs derived from, in Vertebrata, 304;
historical account of views of, 332;
homologies of in the Metazoa, 345

Germinal wall of Chick, 152, 159;
structure and changes of, 160

Geryonia, auditory organ of, 515

Gill of Salpa, 31

Giraldes, organ of, 725

Glands, epidermic, development of, 397

Glomerulus, external, of Chick, 716

Glossopharyngeal nerve, development of, 456, 457

Grey matter of spinal cord, 417;
of brain, 423

Growth in length of Vertebrate embryo, 306

Guinea-pig, primitive streak of, 223;
notochord of, 226;
placenta of, 242;
development of, 262

Gymnophiona, _see_ 'Coecilia'

Habenula perforata, 525

Hairs, development of, 396

Halichærus, placenta of, 250

Hand, 619

Head, comparative account of, 313;
segmentation of, 314

Head cavities, of Elasmobranchii, 50;
Petromyzon, 90, 96;
Amphibia, 127;
general development of, 676

Head-fold of Chick, 157, 167

Head kidney, _see_ 'Pronephros'

Heart, of Pyrosoma, 25;
Elasmobranchii, 50, 58;
Petromyzon, 94, 97;
Acipenser, 106;
Chick, 170;
first appearance of in Rabbit, 230;
general development of, 633;
of Fishes, 635, 637;
of Mammalia, 638;
of Birds, 637, 639;
meaning of development of, 637;
of Amphibia, 638;
of Amniota, 639;
change of position of, 643

Hind-brain, Elasmobranchii, 55, 59, 60;
Petromyzon, 93;
general account of, 424

Hippocampus major, development of, 442

Hirudo, development of blood-vessels of, 633;
excretory organs of, 688

Horse, placenta of, 253

Hyaloid membrane, 492

Hylodes, oviposition of, 121;
metamorphosis of, 137

Hyobranchial cleft, 572

Hyoid arch, of Chick, 179;
general account of, 572, 575;
modifications of, 573, 577;
of Elasmobranchii, 576;
of Teleostei, 577;
of Amphibia, 582;
of Sauropsida, 588;
of Mammalia, 589

Hyomandibular bar of Elasmobranchii, 576, 577;
of Teleostei, 579;
of Amphibia, 582

Hyomandibular cleft, of Petromyzon, 91;
Chick, 179;
general account of, 572

Hyostylic skulls, 582

Hypoblast of Elasmobranchii, 51;
Teleostei, 71, 75;
Petromyzon, 86;
Acipenser, 104;
Lepidosteus, 113;
Amphibia, 122, 129;
Chick, 151, 167;
Lacerta, 203;
Rabbit, 215, 216, 219;
origin of in Rabbit, 220

Hyposkeletal muscles, 675

Hyrax, placenta of, 249

Incus, 529, 590

Infraclavicle, 600

Infundibulum of Petromyzon, 92;
Chick, 175;
general development of, 430

Insectivora, placenta of, 243

Insects, nervous system of, 410;
eye of, 481;
generative organs of, 745;
generative ducts of, 751

Intercalated pieces of vertebral column, 551

Interclavicle, homologies of, 602

Intermediate cell-mass of Chick, 183

Intermuscular septa, 672

Interorbital septum, 570

Interrenal bodies, 665

Iris, 489;
comparative development of, 506

Iris of Ammocoetes, 98

Island of Reil, 444

Jacobson's organ, 537

Jugal bone, 594

Kidney, _see_ 'Metanephros'

Labia majora, development of, 727

Labial cartilages, 597

Labium tympanicum, 525;
vestibulare, 525

Lacertilia, general development of, 202;
nares of, 537;
pectoral girdle of, 603;
pelvic girdle of, 607;
arterial system of, 649

Lacrymal bone, 593

Lacrymal duct, 506

Lacrymal glands, 506

Læmargus, vertebral column of, 548

Lagena, 524

Lamina spiralis, 524

Lamina terminalis, 438

Larva of Amphioxus, 2;
of Ascidia, 15-21;
Teleostei, 81;
Petromyzon, 89, 95;
Lepidosteus, 117, 318;
Amphibia, 134, 142;
types of, in the Invertebrata, 363

Larvæ, nature, origin, and affinities of, 360-386;
secondary variations of less likely to be retained, 362;
ancestral history more fully recorded in, 362;
secondary variations in development of, 363;
ontogenetic record of secondary variations in, 361;
of freshwater and land animals, 362;
types of, 362;
phosphorescence of, 364;
of Coelenterata, 367;
table of, 365;
of Invertebrata, 367 et seq.

Larynx, 766

Lateral line sense organs, 538;
comparison of, with invertebrate, 538;
development of, in Teleostei, 538;
development of, in Elasmobranchii, 539

Lateral ventricle, 438;
anterior cornu of, 440;
descending cornu of, 440;
choroid plexus of, 443

Layers, formation of, in Elasmobranchii, 41, 56;
Teleostei, 71;
Petromyzon, 85;
Acipenser, 103;
Lepidosteus, 111;
Amphibia, 121;
Chick, 150, 152;
Lacerta, 202;
Rabbit, 215-227;
comparison of Mammalia with lower forms, 226, 289;
comparison of formation of in Vertebrata, 275;
origin and homologies of, in the Metazoa, 331

Leech, _see_ 'Hirudo'

Lemuridæ, placenta, 256

Lens, of Elasmobranchii, 57, 58;
Petromyzon, 94, 99;
Acipenser, 106;
Lepidosteus, 115;
Amphibia, 127;
Chick, 177;
of Vertebrate eyes, 485;
general account of, 493;
capsule of, 493;
comparative development of, 499;
of Amphibia, Teleostei, Lepidosteus, 499

Lepidosteus, development of, 111;
larva of, 117;
relations of, 119;
spinal nerves of, 455;
ribs of, 561;
generative ducts of, 704, 735;
swimming-bladder of, 763

Ligamentum pectinatum, 490

Ligamentum suspensorium, 557, 558

Ligamentum vesicæ medium, 239

Limbs, of Elasmobranchii, 59;
Teleostei, 80;
first appearance of in Chick, 184;
Rabbit, 232;
muscles of, 673;
of Fishes, 609;
relation of, to unpaired fins of Fishes, 611, 612;
of Amphibia, 618

Liver of Teleostei, 78;
Petromyzon, 95, 96;
Acipenser, 110;
Amphibia, 130;
general account of, 769

Lizard, development of, 202;
general growth of embryo of, 208;
Müllerian duct of, 721

Lizzia, eye of, 471

Lobi inferiores, 431

Lungs of Amphibia, 137;
development of, 763;
homology of, 766

Lymphatic system, 664

Malleus, 529, 591;
views on, 591

Malpighian bodies, development of accessory in Elasmobranchs, 695

Mammalia, development of, 214;
comparison of gastrula of, 291;
cerebellum of, 427;
infundibulum of, 431;
pineal gland of, 434;
pituitary body of, 436;
cerebrum of, 439;
spinal nerves of, 449;
sympathetic of, 466;
vertebral column of, 558;
branchial arches of, 573, 574;
mandibular and hyoid arches of, 589;
pectoral girdle of, 604;
pelvic girdle of, 608;
heart of, 636;
arterial system of, 647;
venous system of, 661;
muscle-plates of, 671;
mesonephros of, 714;
testicular network of, 724;
urinogenital sinus of, 727;
spermatozoa of, 747;
lungs of, 765;
intestines of, 768;
liver of, 769;
postanal gut of, 774;
stomodæum of, 775

Mammary gland, development of, 398

Man, placenta of, 244;
general account of development of, 265;
characters of embryo of, 270

Mandibular arch of Elasmobranchii, 62, 576;
Petromyzon, 91;
Acipenser, 106, 116;
Chick, 179;
general account of, 572, 575;
modification of to form jaws, 573, 575;
of Teleostei, 580;
of Amphibia, 582;
Sauropsida, 588;
Mammalia, 589

Mandibular bar, evolution of, 311, 321

Manis, placenta of, 256

Marsupial bones, 608

Marsupialia, foetal membranes of, 240;
cerebellum of, 426;
corpus callosum of, 443;
uterus of, 726

Maxilla, 594

Meatus auditorius externus, of Chick, 181;
development of, 527

Meckelian cartilage, of Elasmobranchii, 576;
of Teleostei, 581;
of Amphibia, 584, 585;
of Sauropsida, 588;
of Mammalia, 590

Mediastinum anterior and posterior, 630

Medulla oblongata, of Chick, 176;
general development of, 425

Medullary plate of Amphioxus, 4, 5;
of Ascidia, 11;
Elasmobranchii, 44, 47, 55;
Teleostei, 72;
Petromyzon, 88;
Acipenser, 104;
Lepidosteus, 111;
Amphibia, 126, 127, 131;
Chick, 159;
Lacerta, 204;
Rabbit, 223, 227, 228;
primitive bilobed character of, 303, 317

Medusæ, auditory organs of, 513

Membrana capsulo-pupillaris, 494, 504, 507

Membrana elastica externa, 546

Membrana limitans of retina, 491

Membrana tectoria, 522, 525

Membrane bones, of Amphibia, 582;
of Sauropsida, 588;
of Mammalia, 590;
of mandibular arch, 593;
of pectoral girdle, 599, 602;
origin of, 592;
homologies of, 593

Membranous labyrinth, development of in Man, 519

Menobranchus, branchial arches of, 142

Mesenteron of Elasmobranchii, 43;
Teleostei, 75;
Petromyzon, 85;
Acipenser, 104;
Amphibia, 123, 124, 129;
Chick, 167;
general account of, 754

Mesentery, 626, 756

Mesoblast, of Amphioxus, 6;
Ascidia, 17, 20;
Pyrosoma, 24;
Salpa, 30;
Elasmobranchii, 44, 47;
Teleostei, 75;
Petromyzon, 86;
Acipenser, 105;
Lepidosteus, 113;
Amphibia, 125, 128, 129;
of Chick, 154, 167;
double origin of in Chick, 154, 158, 159;
origin of from lips of blastopore in Chick, 158;
of area vasculosa of Chick, 160;
Lacerta, 203;
origin of in Rabbit, 218, 223;
of area vasculosa in Rabbit, 227;
comparative account of formation of, 292;
discussion of development of in Vertebrata, 297;
meaning of development of in Amniota, 298;
phylogenetic origin of, 346;
summary of ontogeny of, 349-352;
views on ontogeny of, 352-360

Mesoblastic somites, of Amphioxus, 6;
Elasmobranchii, 48, 55;
Petromyzon, 88;
Acipenser, 105;
Lepidosteus, 114;
Amphibia, 129, 131;
Chick, 161, 180;
Rabbit, 228;
development of in Chordata, 325;
meaning of development of, 331;
of head, 676

Mesogastrium, 758

Mesonephros, of Teleostei, 78, 702;
Petromyzon, 95, 98, 700;
Acipenser, 110, 705;
Amphibia, 134, 708;
Chick, 184, 714;
general account of, 690;
development of in Elasmobranchs 691;
of Cyclostomata, 700;
Ganoidei, 705;
sexual and non-sexual part of in Amphibia, 710;
of Amniota, 713, 724;
summary and general conclusions as to, 729;
relation of to pronephros, 731

Mesopterygium, 616

Metagenesis of Ascidians, 34

Metamorphosis of Amphibia, 137, 140

Metanephros, 690;
development of in Elasmobranchii, 697;
of Amphibia, 712;
of Amniota, 713;
of Chick, 722;
of Lacertilia, 723;
phylogeny of, 736

Metapterygium, 616

Metapterygoid, of Elasmobranchii, 576;
of Teleostei, 581

Metazoa, evolution of, 339, 342;
ancestral form of, 333, 345

Mid-brain, of Elasmobranchii, 55, 58, 59;
Petromyzon, 92;
general account of development of, 427

Moina, generative organs of, 745

Molgula, development of, 22

Mollusca, nervous system of, 414;
eyes of, 472;
auditory organs of, 515;
excretory organs of, 681

Monotremata, foetal membranes of, 240;
cerebellum of, 426;
corpus callosum of, 443;
cerebrum of, 443;
urinogenital sinus of, 726

Mormyrus, generative ducts of, 704

Mouth, of Amphioxus, 7;
of Ascidia, 18;
Pyrosoma, 27;
Salpa, 31;
Elasmobranchii, 57, 60, 61, 62;
Petromyzon, 92, 94, 95, 99;
Acipenser, 107;
Lepidosteus, 118;
Amphibia, 129, 132, 134;
Rabbit, 231;
origin of, 317

Mouth, suctorial, of Petromyzon, 99;
Acipenser, 107;
Lepidosteus, 116, 317;
Amphibia, 133, 141, 317

Müllerian duct, 690;
of Elasmobranchs, 693;
of Ganoids, 704;
of Amphibia, 710;
of Aves, 717, 720;
opening of into cloaca, 727;
origin of, 733;
summary of development of, 733;
relation of to pronephros, 733

Muscle-plates, of Amphioxus, 6;
Elasmobranchii, 49, 668;
Teleostei, 670;
Petromyzon, 94;
Chick, 183, 670;
general development of, 669;
of Amphibia, 670;
Aves, 670;
of Mammalia, 671;
origin of muscles from, 672

Muscles, of Ascidia, 11, 17;
development of from muscle-plates, 672;
of limbs, 673;
of head, 676;
of branchial arches, 678;
of eye, 678

Muscular fibres, epithelial origin of, 667

Muscular system, development of, 667;
of Chordata, 668

Mustelus, placenta of, 66

Myoepithelial cells, 667

Mysis, auditory organ of, 517

Myxine, ovum of, 100;
olfactory organ of, 533;
portal sinus of, 652;
excretory system of, 701

Nails, development of, 397

Nares, of Acipenser, 108;
of Ichthyopsida, 534;
development of in Chick, 535;
development of in Lacertilia, 537;
development of in Amphibia, 537

Nasal bones, 592

Nasal pits, Acipenser, 108;
Chick, 176;
general development of, 531

Nematoda, excretory organs of, 689;
generative organs of, 745;
generative ducts of, 752

Nemertines, nervous system of, 311;
excretory organs of, 681

Nerve cord, origin of ventral, 378

Nerves, spinal, 449;
cranial, 455-466

Nervous system, central,
general account of development of in Vertebrata, 415;
conclusions as to, 445;
sympathetic, 466

Nervous system, of Amphioxus, 4;
Ascidia, 15, 16;
Molgula, 22;
Pyrosoma, 24, 25;
Salpa, 30, 31;
Elasmobranchii, 44;
Teleostei, 77;
Petromyzon, 89, 93;
Acipenser, 105;
Amphibia, 126;
comparative account of formation of central, 301;
of Sagitta, 349;
origin of in Coelenterata, 349;
of præoral lobe, 377, 380;
evolution of, 400-405;
development of in Invertebrates, 406;
of Arthropoda, 408;
of Gephyrea, 412;
Mollusca, 414

Neural canal, of Ascidia, 10;
Teleostei, 72;
Petromyzon, 88;
Acipenser, 105;
Lepidosteus, 114;
Amphibia, 126, 131;
Chick, 166, 171;
Lacerta, 208;
closure of in Frog and Amphioxus, 279;
closure of in Elasmobranchii, 284;
phylogenetic origin of, 316

Neural crest, 449, 456, 457

Neurenteric canal, of Amphioxus, 4, 5;
Ascidia, 10;
Elasmobranchii, 54;
Petromyzon, 88;
Acipenser, 105;
Lepidosteus, 113;
Aves, 162;
Lacerta, 203, 206;
general account of, 323;
meaning of, 323

Newt, ovum of, 120;
development of, 125;
general growth of, 141

Notidanus, vertebral column of, 548;
branchial arches of, 572

Notochord of Amphioxus, 6;
Ascidia, 11, 17;
Elasmobranchii, 51;
Teleostei, 74;
Petromyzon 86, 94;
Acipenser, 104;
Lepidosteus, 113;
Amphibia, 128, 129;
Chick, 157;
canal of, in Chick, 163;
Lacerta, 204, 205;
Guinea-pig, 226;
comparative account of formation of, 292, 325;
sheath of, 545;
later histological changes in, 546;
cartilaginous sheath of, 547;
in head, 566;
absence of in region of trabeculæ, 567

Notodelphys, brood-pouch of, 121;
branchiæ of, 140

Nototrema, brood-pouch of, 121

Nucleus pulposus, 559

Oceania, eye of, 471

Occipital bone, 595

OEsophagus, solid, of Elasmobranchii, 61, 759;
of Teleostei, 78

Olfactory capsules, 571

Olfactory lobes, development of, 444

Olfactory nerves, Ammocoetes, 99;
general development of, 464

Olfactory organ, of aquatic forms, 531;
Insects and Crustacea, 531;
of Tunicata, 532;
of Amphioxus, 532;
of Vertebrata, 533;
Petromyzon, 533;
of Myxine, 533

Olfactory sacks, of Elasmobranchii, 60;
Teleostei, 73;
Petromyzon, 92, 97;
Acipenser, 106, 108;
Lepidosteus, 116;
Chick, 176

Oligochæta, excretory organs of, 683

Olivary bodies, 426

Omentum, lesser and greater, 757

Onchidium, eye of, 478

Opercular bones, 593

Operculum, of Teleostei, 77;
Acipenser, 107;
Lepidosteus, 117, 118;
Amphibia, 135

Ophidia, development of, 210;
arterial system of, 649;
venous system of, 656

Optic chiasma, 430, 493

Optic cup, retinal part of, 488;
ciliary portion of, 489

Optic lobes, 428

Optic nerve, development of, 492;
comparative development of, 500

Optic thalami, development of, 431

Optic vesicle, of Elasmobranchii, 57-59;
Teleostei, 74, 499;
Petromyzon, 89, 92;
Acipenser, 106;
Lepidosteus, 115;
Chick, 170;
Rabbit, 229;
general development of, 429;
formation of secondary, 487;
obliteration of cavity of, 488;
comparative development of, 499;
of Lepidosteus and Teleostei, 499.
_See also_ 'Eye'

Ora serrata, 488

Orbitosphenoid region of skull, 570

Organs, classification of, 391;
derivation of from germinal layers, 392

Orycteropus, placenta of, 249

Otic process of Axolotl, 583;
of Frog, 585 et seq.

Otoliths, 512

Oviposition, of Amphioxus, 1;
Elasmobranchii, 40;
Teleostei, 68;
Petromyzon, 84;
Amphibia, 121;
Reptilia, 202

Ovum, of Amphioxus, 1;
Pyrosoma, 23;
Elasmobranchii, 40;
Teleostei, 68;
Petromyzon, 83;
Myxine, 100;
Acipenser, 102;
Lepidosteus, 111;
Amphibia, 120;
Chick, 146;
Reptilia, 202;
Mammalia, 214;
of Porifera, 741;
migration of in Coelenterata, 742;
Vertebrata, 746

Palatine bone, of Teleostei, 580;
origin of, 594

Pancreas, Acipenser, 110;
general development of, 770

Pancreatic cæca, of Teleostei, etc. 768

Papillæ, oral, of Acipenser, 108;
Lepidosteus, 116

Parachordals, 565, 566

Parasphenoid bone, 594

Parepididymis, 725

Parietal bones, 592

Paroophoron, 725

Parovarium, 725

Pectoral girdle, 599;
of Elasmobranchs, 600;
of Teleostei, 600;
of Amphibia and Amniota, 601;
comparison of with pelvic, 608

Pecten, eye of, 479

Pecten, of Ammocoetes, 498;
of Chick, 501;
Lizard, 501;
Elasmobranchs, 501

Pedicle, of Axolotl, 484;
of Frog, 485

Pelobates, branchial apertures of, 136;
vertebral column of, 556

Pelodytes, branchial chamber of, 135

Pelvic girdle, 606;
of Fishes, 606;
Amphibia and Amniota, 607;
of Lacertilia, 607;
of Mammalia, 608;
comparison with pectoral, 608

Penis, development of, 727

Peribranchial cavity, of Amphioxus, 7;
of Ascidia, 18;
Pyrosoma, 24

Pericardial cavity, of Pyrosoma, 26;
Elasmobranchii, 49;
Petromyzon, 94;
general account of, 626;
of Fishes, 627;
of Amphibia, Sauropsida and Mammalia, 628

Perichordal formation of vertebral column, 556

Perilymph of ear, 523

Periotic capsules, ossifications in, 595, 596

Peripatus, nervous system of, 409;
eye of 480;
excretory organs of, 688

Peritoneal membrane, 626

Petromyzon, development of, 83;
affinities of, 83, 84;
general development of, 87;
hatching of, 89;
comparison of gastrula of, 280;
branchial skeleton of, 312, 572;
cerebellum of, 425;
pineal gland of, 434;
pituitary body of, 436;
cerebrum of, 439;
auditory organ of, 517;
olfactory organ of, 533;
comparison of oral skeleton of with Tadpole, 586;
pericardial cavity of, 627;
abdominal pores of, 626;
venous system of, 651;
excretory organs of, 700;
segmental duct of, 700;
pronephros of, 700;
mesonephros of, 700;
thyroid body of, 760;
postanal gut of, 774;
stomodæum of, 775

Phosphorescence of larvæ, 364

Phylogeny, of the Chordata, 327;
of the Metazoa, 384

Pig, placenta of, 251;
mandibular and hyoid arches of, 589

Pineal gland, of Petromyzon, 93;
Chick, 175;
general development of, 432;
nature of, 432, 434

Pipa, brood-pouch of, 121;
metamorphosis of, 139;
yolk-sack of, 140;
vertebral column of, 556

Pituitary body, of Rabbit, 231;
general development of, 435;
meaning of, 436;
Placenta, of Salpa, 29;
Elasmobranchii, 66;
of Mammalia, 232;
villi of, 235;
deciduate and non-deciduate, 239;
comparative account of, 239-259;
characters of primitive type of, 240;
zonary, 248;
non-deciduate, 250;
histology of, 257;
evolution of, 259

Placoid scales, 395

Planorbis, excretory organs of, 681

Planula, structure of, 367

Pleural cavities, 631

Pleuronectidæ, development of, 80

Pneumatocoela, characters of, 327

Polygordius, excretory organs of, 684

Polyophthalmus, eye of, 479

Polypedates, brood-pouch of, 121

Polyzoa, excretory organs of, 682;
generative cells of, 745;
generative ducts of, 751

Pons Varolii, 426, 427

Pori abdominales, Ammocoetes, 99

Porifera, ancestral form of, 345;
development of generative cells of, 741

Portal vein, 653

Postanal gut of Elasmobranchii, 58, 59, 60;
Teleostei, 75;
Chick, 169;
general account of, 323, 772

Præmaxilla, 594

Præopercular bone, 593

Præoral lobe, ganglion of, 377, 380

Prefrontals, 597

Presphenoid region of skull, 570

Primitive groove of Chick, 155

Primitive streak, of Chick, 152, 161;
meaning of, 153;
origin of mesoblast form in Chick, 154;
continuity of hypoblast with epiblast at anterior end of, in
Chick, 156;
comparison of with blastopore, 165;
fate of, in Chick, 165;
of Lacerta, 203;
of Rabbit, 221;
of Guinea-pig, 223;
fusion of layers at, in Rabbit, 224;
comparison of with blastopore of lower forms, 226, 287;
of Mammalia, 290

Processus falciformis of Ammocoetes, 498;
of Elasmobranch, 502;
of Teleostei, 503

Proctodæum, 778

Pronephros, of Teleostei, 78, 701;
Petromyzon, 95, 99, 700;
Acipenser, 106, 110;
Amphibia, 134, 707;
general account of, 689;
of Cyclostomata, 700;
of Myxine, 701;
Ganoidei, 705;
of Amniota, 714;
of Chick, 718;
summary of and general conclusions as to, 728;
relation of, to mesonephros, 731;
cause of atrophy of, 729

Prootic, 596, 597

Propterygium, 616

Proteus, branchial arches of, 142

Protochordata, characters of, 327

Proto-ganoidei, characters of, 328

Proto-gnathostomata, characters of, 328

Proto-pentadactyloidei, characters of, 329

Protovertebrata, characters of, 328

Pseudis, Tadpole of, 139;
vertebral column of, 556

Pseudophryne, yolk-sack of, 140;
Tadpole of, 140

Pterygoid bone, of Teleostei, 581;
origin of, 597

Pterygoquadrate bar, of Elasmobranchii, 576;
of Teleostei, 581;
Axolotl, 584;
Frog, 584;
of Sauropsida, 588;
of Mammalia, 589

Pulmonary artery, origin of, 645;
of Amphibia, 645;
of Amniota, 649

Pulmonary vein, 655

Pupil, 489

Pyrosoma, development of, 23

Quadrate bone of Teleostei, 581;
of Axolotl, 584;
Frog, 585;
Sauropsida, 588

Quadratojugal bone, 594

Rabbit, development of, 214;
general growth of embryo of, 227;
placenta of, 248

Radiate symmetry, passage from to bilateral symmetry, 373-376

Raja, caudal vertebræ of, 553

Rat, placenta of, 242

Recessus labyrinthi, 519

Reissner's membrane, 524

Reptilia, development of, 202;
viviparous, 202;
cerebellum of, 426;
infundibulum of, 431;
pituitary body of, 436;
cerebrum of, 439;
vertebral column of, 556;
arterial system of, 648;
venous system of, 656;
mesonephros of, 713;
testicular network of, 723;
spermatozoa of, 747

Restiform tracts of Elasmobranchii and Teleostei, 425

Retina, histogenesis of, 490

Retinulæ, 482

Rhabdom, 482

Rhinoderma, brood-pouch of, 121;
metamorphosis of, 139

Ribs, development of, 560

Rosenmüller's organ, 725

Rotifera, excretory organs of, 680

Round ligament of liver, 663

Ruminantia, placenta of, 253

Sacci vasculosi, 437

Sacculus hemisphericus, 519;
of Mammals, 519, 520

Sagitta. _See_ 'Chætognatha'

Salpa, sexual development of, 29;
asexual development of, 33

Salamandra, larva of, 142;
vertebral column of, 553;
limbs of, 619;
mesonephros of, 708;
Müllerian duct of, 710

Salmonidæ, hypoblast of, 71;
generative ducts of, 704

Sauropsida, gastrula of, 286;
meaning of primitive streak of, 288;
blastopore of, 289;
mandibular and hyoid arches of, 588;
pectoral girdle of, 601

Scala, vestibuli, 522;
tympani, 523;
media, 522

Scales, general development of, 396;
development of placoid scales, 395

Scapula, 599

Sclerotic, 488

Scrotum, development of, 727

Scyllium, caudal vertebræ of, 553;
mandibular and hyoid arches of, 578;
pectoral girdle of, 600;
limbs of, 610;
pelvic fin of, 614;
pectoral fin of, 615

Segmental duct, 690;
development of in Elasmobranchs, 690;
of Cyclostomata, 700;
of Teleostei, 701;
of Ganoidei, 704, 705;
of Amphibia, 707;
of Amniota, 713

Segmental organs, 682

Segmental tubes, 690;
development of in Elasmobranchs, 691;
rudimentary anterior in Elasmobranchs, 693;
development of secondary, 731

Segmentation cavity, of Elasmobranchii, 42-44;
Teleostei, 69, 85, 86;
Amphibia, 122, 125

Segmentation, meaning of, 331

Segmentation of ovum, in Amphioxus, 2;
Ascidia, 9;
Molgula, 22;
Pyrosoma, 23;
Salpa, 30;
Elasmobranchii, 40;
Telostei, 69;
Petromyzon, 84;
Acipenser, 102;
Lepidosteus, 111;
Amphibia, 122, 124;
Newt, 125;
Chick, 146;
Lizard, 202;
Rabbit, 214

Semicircular canals, 519

Sense organs, comparative account of development of, 304

Septum lucidum, 443

Serous membrane, Lacerta, 209;
of Rabbit, 237

Seventh nerve, development of, 459

Shell-gland of Crustacea, 689

Shield, embryonic, of Chick, 151;
of Lacerta, 202

Simiadæ, placenta of, 247

Sinus rhomboidalis, of Chick, 162

Sinus venosus, 637

Sirenia, placenta of, 255

Sixth nerve, 463

Skate, mandibular and hyoid arches of, 577

Skeleton, elements of found in Vertebrata, 542

Skull, general development of, 564;
historical account of, 564;
development of cartilaginous, 566;
cartilaginous walls of, 570;
composition of primitive cartilaginous cranium, 565

Somatopleure, of Chick, 170

Spelerpes, branchial arches of, 142

Spermatozoa, of Porifera, 741;
of Vertebrata, 746

Sphenoid bone, 595

Sphenodon, hyoid arch of, 588

Spinal cord, general account of, 415;
white matter of, 415;
central canal of, 417, 418;
commissures of, 417;
grey matter of, 417;
fissures of, 418

Spinal nerves, posterior roots of, 449;
anterior roots of, 453

Spiracle, of Elasmobranchii, 62;
Acipenser, 105;
Amphibia, 136

Spiral valve. _See_ 'Valve'

Spleen, 664

Splenial bone, 595

Squamosal bone, 593

Stapes, 529;
of Mammal, 590

Sternum, development of, 562

Stolon of Doliolum, 29;
Salpa, 33

Stomodæum, 774

Stria vascularis, 524

Styloid process, 591

Subintestinal vein, 651;
meaning of, 651

Syngnathus, brood-pouch of, 68

Subnotochordal rod, of Elasmobranchii, 54;
Petromyzon, 94;
Acipenser, 110;
Lepidosteus, 115;
general account of, 754;
comparison of with siphon of Chætopods, 756

Subzonal membrane, 237;
villi of, 236

Sulcus of Munro, 432

Supraclavicle, 600

Suprarenal bodies, 664

Supra-temporal bone, 593

Swimming bladder, _see_ Air bladder

Sylvian aqueduct, 428

Sylvian fissure, 444

Sympathetic ganglia, development of, 467

Tadpole, 134, 139, 140;
phylogenetic meaning of, 137;
metamorphosis of, 137;
meaning of suctorial mouth of, 585

Tail of Teleostei, 80;
Acipenser, 109;
Lepidosteus, 109;
Amphibia, 132

Tarsus, development of, 620

Teeth, horny provisional, of Amphibia, 136;
general development of, 776;
origin of, 777

Teleostei, development of, 68;
viviparous, 68;
comparison of formation of layers in, 286;
restiform tracts of, 425;
mid-brain of, 425;
infundibulum of, 431;
cerebrum of, 439;
nares of, 534;
lateral line of, 538;
notochord and membrana elastica of, 549;
vertebral column of, 553;
ribs of, 561;
hyoid and mandibular arches of, 579;
pectoral girdle of, 601;
pelvic girdle of, 606;
limbs of, 618;
heart of, 637;
arterial system of, 645;
muscle-plates of, 670;
excretory organs of, 701;
generative ducts of, 704, 735, 749;
swimming bladder of, 763;
postanal gut of, 774

Teredo, nervous system of, 414

Test of Ascidia, 14;
Salpa, 31

Testicular network, of Elasmobranchs, 697;
of Amphibia, 712;
Reptilia, 723;
of Mammals, 724

Testis of Vertebrata, 746

Testis, connection of with Wolffian body, in Elasmobranchii, 697;
in Amphibia, 710;
in Amniota, 723;
origin of, 735

Thalamencephalon of Chick, 175;
general development of, 430

Third nerve, development of, 461

Thymus gland, 762

Thyroid gland, Petromyzon, 92;
general account of, 759;
nature of, 760;
development of in Vertebrata, 761

Tooth. _See_ 'Teeth'

Tori semicirculares, 428

Tornaria, 372

Trabeculæ, 565, 567;
nature of, 568

Trachea, 766

Trematoda, excretory organs of, 681

Triton alpestris, sexual larva of, 143

Triton, development of limbs of, 619;
urinogenital organs of, 712

Truncus arteriosus, 638;
of Amphibia, 638;
of Birds, 639

Tunicata, development of mesoblast of, 293;
test of, 394;
eye of, 507;
auditory organ of, 530;
olfactory organ of, 532;
generative duct of, 749;
intestine of 767;
postanal gut of, 771;
stomodæum of, 775

Turbellaria, excretory organs of, 681

Tympanic annulus of Frog, 587

Tympanic cavity, of Amphibia, 135;
Chick, 180;
Rabbit, 232;
general development of, 528;
of Mammals, 591

Tympanic membrane, of Chick, 180;
general development of, 528

Tympanohyal, 591

Umbilical canal of Elasmobranchii, 54, 57, 58, 59

Umbilical cord, 238;
vessels of, 239

Ungulata, placenta of, 250

Urachus, 239, 726

Ureters, of Elasmobranchii, 696;
development of, 723

Urethra, 727

Urinary bladder of Amphibia, 712;
of Amniota, 726

Urinogenital organs, _see_ Excretory organs

Urinogenital sinus of Petromyzon, 700;
of Sauropsida, 726;
of Mammalia, 727

Urochorda, development of, 9

Uterus, development of, 726;
of Marsupials, 726

Uterus masculinus, 726

Utriculus, 519

Uvea of iris, 489

Vagus nerve, development of, 456, 457;
intestinal branch of, 458;
branch of to lateral line, 459

Valve, spiral, of Petromyzon, 97;
Acipenser, 110;
general account of, 767

Valves, semilunar, 641;
auriculo-ventricular, 642

Vasa efferentia, of Elasmobranchs, 697;
of Amphibia, 711;
general origin of, 724

Vascular system, of Amphioxus, 8;
Petromyzon, 97;
Lepidosteus, 116;
general development of, 632

Vas deferens, of Elasmobranchii, 697;
of Amniota, 723

Vein, subintestinal of Petromyzon, 97;
Acipenser, 110;
Lepidosteus, 116

Velum of Petromyzon, 91

Vena cava inferior, development of, 655

Venous system of Petromyzon, 97;
general development of, 651;
of Fishes, 651;
of Amphibia and Amniota, 655;
of Reptilia, 656;
of Ophidia, 656;
of Aves, 658;
of Mammalia, 661

Ventricle, fourth, of Chick, 176;
history of, 424

Ventricle, lateral, 438, 440;
fifth, 443

Ventricle, third, of Chick, 175

Vertebral bodies, of Chick, 183

Vertebral column, development of, 545, 549;
epichordal and perichordal development of in Amphibia, 556

Vespertilionidæ, early development of, 217

Vieussens, valve of, 426

Villi, placental, of zona radiata, 235;
subzonal membrane, 235;
chorion, 237;
Man, 246;
comparative account of, 257;
of young human ovum, 265, 269

Visceral arches, Amphioxus, 7;
Elasmobranchii, 57-60;
Teleostei, 77;
Acipenser, 106;
Lepidosteus, 116;
Amphibia, 133;
Chick, 177;
Rabbit, 231;
præoral, 570;
relation of to head cavities, 572;
disappearance of posterior, 573;
dental plates of in Teleostei, 574

Visual organs, evolution of, 470

Vitelline arteries of Chick, 195

Vitelline veins of Chick, 195

Vitreous humour, of Ammocoetes, 98;
general development of, 494;
blood-vessels of in Mammals 503;
mesoblastic ingrowth in Mammals, 503

Vomer, 594

White matter, of spinal cord, 415;
of brain, 423

Wolffian body, _see_ 'Mesonephros'

Wolffian duct, first appearance of in Chick, 183;
general account of, 690;
of Elasmobranchs, 693;
of Ganoids, 704;
of Amphibia, 710;
of Amniota, 713;
atrophy of in Amniota, 724

Wolffian ridge, 185

Yolk blastopore, of Elasmobranchii, 64

Yolk, folding off of embryo from, in Elasmobranchii, 55;
in Teleostei, 76;
Acipenser, 106;
Chick, 168, 170

Yolk nuclei, of Elasmobranchii, 41, 53;
Teleostei, 69, 75

Yolk, of Elasmobranchii, 40;
Teleostei, 68;
Petromyzon, 96;
Acipenser, 109;
Amphibia, 122, 129;
Chick, 146;
influence of on formation of layers, 278;
influence of on early development, 341, 342

Yolk-sack, Amphibia, 131, 140, 141;
enclosure of, 123

Yolk-sack, development of in Rabbit, 227;
of Mammalia reduced, 227;
circulation of in Rabbit, 233;
enclosure of in Sauropsida, 289

Yolk-sack, enclosure of, Petromyzon, 86

Yolk-sack, Lepidosteus, 118

Yolk-sack of Chick, enclosure of, 160;
stalk of, 174;
general account of, 193;
circulation of, 195;
later history of, 198

Yolk-sack of Elasmobranchii, enclosure of, 62, 283;
circulation of, 64

Yolk-sack of Lacerta, 209;
circulation of, 209

Yolk-sack, Teleostei, 75, 81;
enclosure of, 75;
circulation of, 81

Zona radiata, villi of, 237

Zonula of Zinn, 495

BIBLIOGRAPHY.

CEPHALOPODA.

(1) A. Kowalevsky. "Entwicklungsgeschichte des Amphioxus lanceolatus." _Mém. Acad. Impér. des Sciences de St Pétersbourg_, Series VII. Tom. XI. 1867.

(2) A. Kowalevsky. "Weitere Studien über die Entwicklungsgeschichte des Amphioxus lanceolatus." _Archiv f. mikr. Anat._, Vol. XIII. 1877.

(3) Leuckart u. Pagenstecher. "Untersuchungen über niedere Seethiere." _Müller's Archiv_, 1858.

(4) Max Schultze. "Beobachtung junger Exemplare von Amphioxus." _Zeit. f. wiss. Zool._, Bd. III. 1851.

(5) A. M. Marshall. "On the mode of Oviposition of Amphioxus." _Jour. of Anat. and Phys._, Vol. X. 1876.

UROCHORDA.

(6) P. J. van Beneden. "Recherches s. l'Embryogénie, l'Anat. et la Physiol. des Ascidies simples." _Mém. Acad. Roy. de Belgique_, Tom. XX.

(7) W. K. Brooks. "On the development of Salpa." _Bull. of the Museum of Comp. Anat. at Harvard College, Cambridge, Mass._

(8) H. Fol. _Etudes sur les Appendiculaires du détroit de Messine._ Genève et Bâle, 1872.

(9) Ganin. "Neue Thatsachen a. d. Entwicklungsgeschichte d. Ascidien." _Zeit. f. wiss. Zool._, Vol. XX. 1870.

(10) C. Gegenbaur. "Ueber den Entwicklungscyclus von Doliolum nebst Bemerkungen über die Larven dieser Thiere." _Zeit. f. wiss. Zool._, Bd. VII. 1856.

(11) A. Giard. "Etudes critiques des travaux d'embryogénie relatifs à la parenté des Vertébrés et des Tuniciers." _Archiv Zool. expériment._, Vol. I. 1872.

(12) A. Giard. "Recherches sur les Synascidies." _Archiv Zool. expér._, Vol. I. 1872.

(13) O. Hertwig. "Untersuchungen üb. d. Bau u. d. Entwicklung des Cellulose-Mantels d. Tunicaten." _Jenaische Zeitschrift_, Bd. VII. 1873.

(14) Th. H. Huxley. "Remarks upon Appendicularia and Doliolum." _Phil. Trans._, 1851.

(15) Th. H. Huxley. "Observations on the anatomy and physiology of Salpa and Pyrosoma." _Phil. Trans._, 1851.

(16) Th. H. Huxley. "Anatomy and development of Pyrosoma." _Linnean Trans._, 1860, Vol. XXIII.

(17) Keferstein u. Ehlers. _Zoologische Beiträge_, 1861. Doliolum.

(18) A. Kowalevsky. "Entwicklungsgeschichte d. einfachen Ascidien." _Mém. Acad. Pétersbourg_, VII. série, T. X. 1866.

(19) A. Kowalevsky. "Beitrag z. Entwick. d. Tunicaten." _Nachrichten d. königl. Gesell. zu Göttingen._ 1868.

(20) A. Kowalevsky. "Weitere Studien üb. d. Entwicklung d. einfachen Ascidien." _Archiv f. mikr. Anat._, Vol. VII. 1871.

(21) A. Kowalevsky. "Ueber Knospung d. Ascidien." _Archiv f. mikr. Anat._, Vol. X. 1874.

(22) A. Kowalevsky. "Ueber die Entwicklungsgeschichte d. Pyrosoma." _Archiv f. mikr. Anat._, Vol. XI. 1875.

(23) A. Krohn. "Ueber die Gattung Doliolum u. ihre Arten." _Archiv f. Naturgeschichte_, Bd. XVIII. 1852.

(24) A. Krohn. "Ueber die Entwicklung d. Ascidien." _Müller's Archiv_, 1852.

(25) A. Krohn. "Ueber die Fortpflanzungsverhältnisse d. Botrylliden." _Archiv f. Naturgeschichte_, Vol. XXXV. 1869.

(26) A. Krohn. "Ueber die früheste Bildung d. Botryllenstöcke." _Archiv f. Naturgeschichte_, Vol. XXXV. 1869.

(27) C. Kupffer. "Die Stammverwandschaft zwischen Ascidien u. Wirbelthieren." _Archiv f. mikr. Anat._, Vol. VI. 1870.

(28) C. Kupffer. "Zur Entwicklung d. einfachen Ascidien." _Archiv f. mikr. Anat._, Vol. VIII. 1872.

(29) H. Lacaze Duthiers. "Recherches sur l'organisation et l'Embryogénie des Ascidies (Molgula tubulosa)." _Comptes rendus_, May 30, 1870, p. 1154.

(30) H. Lacaze Duthiers. "Les Ascidies simples des Côtes de France" (Development of Molgula). _Archiv Zool. expér._, Vol. III. 1874.

(31) R. Leuckart. "Salpa u. Verwandte." _Zoologische Untersuchungen_, Heft II.

(32) E. Metschnikoff. "Observations sur le développement de quelques animaux (Botryllus and Simple Ascidians)." _Bull. d. l'Acad. Pétersbourg_, Vol. XIII. 1869.

(33) H. Milne-Edwards. "Observations s. l. Ascidies composées des côtes de la Manche." _Mémoires d. l'Institut_, T. XVIII. 1842.

(34) W. Salensky. "Ueber d. embryonale Entwicklungsgeschichte der Salpen." _Zeit. f. wiss. Zool._, B. XXVII. 1877.

(35) W. Salensky. "Ueber die Knospung d. Salpen." _Morphol. Jahrbuch_, Bd. III. 1877.

(36) W. Salensky. "Ueber die Entwicklung d. Hoden u. über den Generationswechsel d. Salpen." _Zeit. f. wiss. Zool._, Bd. XXX. Suppl. 1878.

(37) C. Semper. "Ueber die Entstehung d. geschichteten Cellulose-Epidermis d. Ascidien." _Arbeit. a. d. zool.-zoot. Instit. Würzburg_, Vol. II. 1875.

(38) Fr. Todaro. _Sopra lo sviluppo e l'anatomia delle Salpe._ Roma, 1875.

(39) Fr. Todaro. "Sui primi fenomeni dello sviluppo delle Salpe." _Reale Accademia dei Lincei_, Vol. IV. 1880.

ELASMOBRANCHII.

(40) F. M. Balfour. "A preliminary account of the development of the Elasmobranch Fishes." _Quart. J. of Micr. Science_, Vol. XIV. 1876.

(41) F. M. Balfour. "A Monograph on the development of Elasmobranch Fishes." London, 1878. Reprinted from the _Journal of Anat. and Physiol._ for 1876, 1877, and 1878.

(42) Z. Gerbe. "_Recherches sur la segmentation de la cicatrule et la formation des produits adventifs de l'oeuf des Plagiostomes et particuliérement des Raies._" Vide also _Journal de l'Anatomie et de la Physiologie_, 1872.

(43) W. His. "Ueb. d. Bildung v. Haifischenembryonen." _Zeit. für Anat. u. Entwick._, Vol. II. 1877.

(44) A. Kowalevsky. "Development of Acanthias vulgaris and Mustelus lævis." (Russian.) _Transactions of the Kiew Society of Naturalists_, Vol. I. 1870.

(45) R. Leuckart. "Ueber die allmählige Bildung d. Körpergestalt bei d. Rochen." _Zeit. f. wiss. Zool._, Bd. II., p. 258.

(46) Fr. Leydig. _Rochen u. Haie._ Leipzig, 1852.

(47) A. W. Malm. "Bidrag till kännedom om utvecklingen af Rajæ." _Kongl. vetenskaps akademiens forhandlingar._ Stockholm, 1876.

(48) Joh. Müller. _Glatter Haie des Aristoteles und über die Verschiedenheiten unter den Haifischen und Rochen in der Entwicklung des Eies._ Berlin, 1840.

(49) S. L. Schenk. "Die Eier von Raja quadrimaculata innerhalb der Eileiter." _Sitz. der k. Akad. Wien_, Vol. LXXIII. 1873.

(50) Alex. Schultz. "Zur Entwicklungsgeschichte des Selachiereies." _Archiv für micro._ Anat., Vol. XI. 1875.

(51) Alex. Schultz. "Beitrag zur Entwicklungsgeschichte d. Knorpelfische." _Archiv für micro. Anat._, Vol. XIII. 1877.

(52) C. Semper. "Die Stammesverwandschaft d. Wirbelthiere u. Wirbellosen." _Arbeit. a. d. zool.-zoot. Instit. Würzburg_, Vol. II. 1875.

(53) C. Semper. "Das Urogenitalsystem d. Plagiostomen, etc." _Arbeit. a. d. zool.-zoot. Instit. Würzburg_, Vol. II. 1875.

(54) Wyman. "Observations on the Development of Raja batis." _Memoirs of the American Academy of Arts and Sciences_, Vol. IX. 1864.

TELEOSTEI.

(55) Al. Agassiz. "On the young Stages of some Osseous Fishes. I. Development of the Tail." _Proceedings of the American Academy of Arts and Sciences_, Vol. XIII. Presented Oct. 11, 1877.

(56) Al. Agassiz. "II. Development of the Flounders." _Proceedings of the American Acad. of Arts and Sciences_, Vol. XIV. Presented June, 1878.

(57) K. E. v. Baer. _Untersuchungen über die Entwicklungsgeschichte der Fische._ Leipzig, 1835.

(58) Ch. van Bambeke. "Premiers effets de la fécondation sur les oeufs de Poissons: sur l'origine et la signification du feuillet muqueux on glandulaire chez les Poissons Osseux." _Comptes Rendus des Séances de l'Académie des Sciences_, Tome LXXIV. 1872.

(59) Ch. van Bambeke. "Recherches sur l'Embryologie des Poissons Osseux." _Mém. couronnés et Mém. de savants étrangers de l'Académie roy. Belgique_, Vol. XL. 1875.

(60) E. v. Beneden. "A contribution to the history of the Embryonic development of the Teleosteans." _Quart. J. of Micr. Sci._, Vol. XVIII. 1878.

(61) E. Calberla. "Zur Entwicklung des Medullarrohres u. d. Chorda dorsalis d. Teleostier u. d. Petromyzonten." _Morphologisches Jahrbuch_, Vol. III. 1877.