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.