Org"ns, vital, 57
Origin of alimentary canal, 444
Ori"in of arthropods from annelids, 395
Ori"in of atrial cavity, 409
Ori"in of auditory capsules and parachordals, 377
Ori"in of ductless glands, 428
Ori"in of free cells, 472
Ori"in of heart of vertebrate, 179
Ori"in of lateral line organs, 356
Ori"in of muscles, 478
Ori"in of musculature, branchial, 170
Ori"in of muscul"ture, somatic trunk, 406
Ori"in of nervous system, central, 480
Ori"in of notochord, 434
Ori"in of segmental excretory organs, 389
Ori"in of skeleton of vertebrates, 119
Ori"in of vertebrates, 9, 36, 351, 433, 493
Osteostraci, 29, 75, 275, 326, 343
Otoliths, 378
Ovum, 473
Palæontology, evidence of, 20, 497
Palæostoma, 317
Palæo"traca, median eyes, 74
Palæo"traca, mesosomatic appendages, 188
Palæo"traca, olfactory organs, 221
Palæo"traca, segments, compared to Ammocœtes, 308
Pantopoda, glands, 423
Parapodia, 357
Parapodopsis, foot glands, 422
Parathymus, 427
Parathyroids, 427
Parietal organ, 76
Pecten of scorpion, 114, 359, 366, 371, 372, 373, 374
Pedipalpi, 190
Periblast, 471
Peripatus, 396, 399, 400, 411, 421, 429
Petromyzon, alimentary canal, 405, 445
Petro"mzon, auditory organ, 378
Petro"mzon, branchial segments, 169
Petro"mzon, life-history, 59
Petro"mzon, olfactory tube, 219, 226
Petro"mzon, pronephric duct, 402
Petro"mzon, retina and optic nerve, 95
Petro"mzon, skeleton, 125
Petro"mzon, suctorial apparatus, 287, 304
Petro"mzon, transformation, v. Transformation of the Lamprey
Pharynx of Amphioxus, 410
Phar"nx of Vertebrate, 440
Phoronis, 439
Phrynus, brain, 53
Phry"us, caudal brain, 450
Phry"us, carapace and carapace removed, 250
Phry"us, cœcal diverticula, 109
Phry"us, evidence of segmentation of carapace, 249, 250, 341
Phry"us, operculum, 191
Phry"us, prosomatic appendages, 306
Phry"us, crossing of dorso-ventral muscles, 271, 277
Phry"us, stridulating apparatus, 368
Phyllodoce, 395
Phyllopoda, 321
Pigment, in Ammocœtes, in position of atrial cavity, 412
Pigm"nt, in epithelial lining of central nervous system, 43, 457
Pigm"nt, in choroid of vertebrate eye, 104, 107
Pigm"nt, in between glandular cells round brain of Ammocœtes, 211, 379
Pigm"nt, in tapetal layer of retina, 70
Pigm"nt, in white, of right pineal eye of Lamprey, 76, 80
Pin"al ey"s, of Ammocœtes, 80, 78, 85
Pits, epithelial, of diaphragms in Ammocœtes, 164
Pi"t, epith"lial, of skin in Ammocœtes, 173, 200
Pituitary body, 244, 246, 319, 321, 425, 430
Plasma-cells, 471
Plakodes, 283
Planarians, 475
Plastron, formation of cranial walls from the, 86, 322, 341
Plat"ron, of Limulus, 136, 142, 143
Plat"ron, Palæostracan, compared to trabeculæ of Ammocœtes, 145, 377
Plat"ron, muscles attached to the, 270
Plat"ron, of Thelyphonus, 143
Platyhelmia, 475
Plexus, of Auerbach, 447
Plex"s, of choroid, 38, 45, 49, 103
Plex"s, of hypogastric, 3
Pores, abdominal, 430
Porifera, 473
Pouch, formation of gill, 165, 166
Principle of concentration and cephalization, 51
Prini"ple of embryology, 455
Pristiurus, 424
Progress, law of, 19
Progr"ss, result of, 56
Pronephros, 389, 397, 419, 424, 449
Prosencephalon, 48
Prosoma, 52
Protopterus, 148
Proto"traca, dominance of, 28
Pteraspis, 29, 30, 275, 326, 343, 344, 350
Pterichthys, 29, 31, 239, 326, 351
Pterygoid, pedicle of, 295
Pterygotus, 25, 27, 56, 170, 191, 221, 235, 238, 249, 276
Ramus branchialis profundus of facial nerve, 311
Raphe, 46
Recapitulation, law of, 434, 456, 498
Regeneration of nerves, 469
Reptiles, dominance of, 21
Retina, compound, 71
Ret"ia, development of, 101
Ret"ia, inversion of, in Vertebrates, 114
Ret"ia, inverted, 70
Ret"ia, layers of compound, 73
Ret"ia, lay"rs of in Crustacean eye, 100
Ret"ia, of lateral eye of Ammocœtes, 93, 95, 111
Ret"ia, Musca, 89
Ret"ia, Pecten and Spondylus, 114
Ret"ia, upright compound, 72
Ret"ia, upri"ht simple, 69
Scales, 345
Scaphaspis, 349
Schwann, sheath of, 469
Sclerotomes, 388
Scorpion, brain, 54
Scor"ion, branchial lamellæ, 175
Scor"ion, development, 482
Scor"ion, entochondrites, 377
Scor"ion, excretory organs, 397
Scor"ion, eyes, 75
Scor"ion, lung-books, 150, 170
Scor"ion, lymphatic glands, 423
Scor"ion, muscles, oblique, 278
Scor"ion, mus"les, recti, 271
Scor"ion, mus"les, respiration, 171
Scor"ion, mus"les, veno-pericardial, 177
Scor"ion, muscular system, 247, 268, 269
Scor"ion, nerves to Cheliceræ, 237
Scor"ion, olfactory organs, 220
Scor"ion, operculum of male, 189, 206, 212
Scor"ion, pecten, 359, 366, 371, 373, 374, 377
Scor"ion, under surface, 372
Scor"ion, uterus, 189, 202, 203, 204, 205, 212
Sea-scorpions, 25, 26, 27, 56, 150, 170, 191, 208, 221, 232, 235, 241, 349, 359
Segmentation, branchiomeric, 124
Segmet"ation, body-muscles in vertebrate, 388
Segmet"ation, eye-muscles, 248
Segmet"ation, of head, double, 155, 157, 173, 234, 258, 411, 459
Segmet"ation, of head-shield, 339
Segmet"ation, history of cranial, 258
Segments, branchial of Ammocœtes, 161, 178, 186
Segm"nts, hyoid, in Ammocœtes, double, 186, 201, 267, 300
Segm"nts, innervation of branchial, 151
Segm"nts, first mesosomatic, in Limulus and its allies, 188
Segm"nts, mesosomatic, of Eurypterus, 192
Segm"nts, prosomatic of Limulus and its allies, 233, 249
Segm"nts, prosm"atic of Ammocœtes, 286
Segm"nts, of spinal region of Vertebrates, 388
Segm"nts, of trigeminal nerve-group, 257, 279
Segm"nts, tubular muscles of hyoid, 299
Sense-organs of Amphioxus, 34
Sense-o"rans of branchial, of Limulus, 359, 360
Sense-o"rans of lateral, of Annelids, 357, 367
Sense-o"rans of lateral-line system, 356, 411, 470
Serum, 492
Significance of the optic diverticula, 102
Silurus, 488
Sinus, longitudinal venous, of Limulus, 176, 312, 451
Sin"s, rhomboidal of bird, 46
Skeleton, Ammocœtes, 126, 296, 335
Skel"ton, Amm"cœtes, branchial, 126, 126
Skel"ton, Amm"cœtes, basi-cranial, 132
Skel"ton, Amm"cœtes, muco-cartilaginous, 291, 296, 330, 331
Skel"ton, aponeurotic, 414
Skel"ton, Cephalaspis, 414, 415
Skel"ton, evidence of the, 119
Skel"ton, Limulus, cartilaginous, 126, 136
Skel"ton, Lim"lus, mesosomatic, 137
Skel"ton, Lim"lus, prosomatic, 142
Skel"ton, Petromyzon, 125
Skel"ton, Vertebrate, commencement of bony, 120, 121
Skin, digestive power of cells of, in Ammocœtes, 58, 442
Si"n, of Ammocœtes, 346
Si"n, nerves of, 448
Skull of dogfish, 123
Skl"l of pig-embryo, 121
Slimonia, 27, 56, 170, 235, 238, 249, 276, 303
Solpugidæ, 109
Sphæroma serratum, brain, 62, 90, 101, 225
Spiders, eyes, 75
Spi"ers, stomach, 109
Spina bifida, 50
Spinal cord, difference between brain and, 45
Spi"al cr"d, region of, 385
Spi"al cr"d, termination in bird-embryo, 51
Spondylus, retina of, 114
Squilla, eyes, 100
Sqi"lla, glands, 422
Stomach, cephalic, 4, 43, 102, 244
Stylonurus Lagani, 27, 235, 239, 249
Substantia gelatinosa Rolandi, 44
Suprarenal body, 423
Surfaces, dorsal and ventral, 11
Surf"ces, reversal of, 15, 29, 36, 87, 175, 352, 433, 484
Synapse, 72
Tail of lizards, 50
Tapetum, 69
Teleosteans, 23, 345, 420, 424
Tendon-organs, 470
Tentacles of Ammocœtes, 246, 289, 303
Tergo-coxal muscles, 247
Test, biological, of relationship of animals, 492
Thalainencephalon, 48
Thelodus, 344
Thelyphonus, 231
Thely"honus, brain, 53, 54, 56, 224
Thely"honus, br"in, caudal, 450
Thely"honus, cœcal diverticula, 109
Thely"honus, entosternite, 143
Thely"honus, genital organs, 206
Thely"honus, lyriform organs, 368
Thely"honus, olfactory passage, 226, 306
Thely"honus, operculum, 189, 190, 206, 207
Theories of the origin of vertebrates, 9, 411, 433, 457
Thionin reaction, 131, 139, 213, 330, 336
Throat, formation of, 179
Thyestes, 30, 31, 275, 326, 328, 329, 339, 340, 341
Thyroid gland of Ammocœtes, 61, 127, 192, 194, 196, 429, 459
Thyr"id gl"nd evidence of the, 185
Thyr"id gl"nd function of, in Ammocœtes, 213
Tissues, connective, 471, 474, 481
Tiss"es, evolution of, 19
Tiss"es, notochordal, 435
Tiss"es, two groups of, 463