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.