General history of the Ovum, pp. 17-25. Special history of the Ovum in different types, pp. 26-65. The Spermatozoon, pp. 65-67. CHAPTER II. THE MATURATION AND IMPREGNATION OF THE OVUM. Maturation of the Ovum, and formation of the polar bodies, pp. 68-79. Impregnation of the Ovum, pp. 79-86. Summary, p. 86. CHAPTER III. THE SEGMENTATION OF THE OVUM. Internal phenomena of Segmentation, pp. 88-92. External features of Segmentation, pp. 92-122. INTRODUCTION TO SYSTEMATIC EMBRYOLOGY. Pp. 125-130. CHAPTER IV. DICYEMIDÆ AND ORTHONECTIDÆ. Pp. 131-137. CHAPTER V. PORIFERA. Pp. 138-151. CHAPTER VI. COELENTERATA. Hydrozoa, pp. 152-167. Actinozoa, pp. 167-173. Ctenophora, pp. 173-178. Summary, etc., pp. 178-182. Alternations of generations, pp. 182-187. CHAPTER VII. PLATYELMINTHES. Turbellaria, pp. 189-196. Nemertea, pp. 196-204. Trematoda, pp. 205-210. Cestoda, pp. 210-218. CHAPTER VIII. ROTIFERA. Pp. 221-224. CHAPTER IX. MOLLUSCA. Formation of the layers and larval characters, pp. 225-273. _Gasteropoda and Pteropoda_, pp. 225-242. _Cephalopoda_, pp. 242-254. _Polyplacophora_, pp. 254-257. _Scaphopoda_, pp. 257, 258. _Lamellibranchiata_, pp. 258-269. _General review of Molluscan Larvæ_, pp. 270-273. Development of organs, pp. 273-288. CHAPTER X. POLYZOA. Entoprocta, pp. 292-297. Ectoprocta, pp. 297-305. Summary and general considerations, pp. 305-308. CHAPTER XI. BRACHIOPODA. Development of the layers, pp. 311-313. The history of the larva, pp. 313-317. Development of organs, p. 317. General observations on the affinities of the Brachiopoda, pp. 317, 318. CHAPTER XII. CHÆTOPODA. Formation of the germinal layers, pp. 319-325. The larval form, pp. 325-338. Formation of organs, pp. 338-342. Alternations of generations, pp. 342, 343. CHAPTER XIII. DISCOPHORA. Formation of layers, pp. 347-350. History of larva, pp. 351-354. CHAPTER XIV. GEPHYREA. Gephyrea nuda, pp. 355-361. Gephyrea tubicola, pp. 361-364. General considerations, p. 364. CHAPTER XV. Chætognatha, pp. 366-369. Myzostomea, pp. 369, 370. Gastrotricha, p. 370. CHAPTER XVI. Nematelminthes, pp. 370-379. Acanthocephala, pp. 379-381. CHAPTER XVII. TRACHEATA. Prototracheata, pp. 382-387. Myriapoda, pp. 387-395. Insecta, pp. 395-429. _Embryonic membranes and the formation of the layers_, pp. 400-406. _Formation of the organs_, pp. 406-417. _Special types of larvæ_, pp. 417-419. _Metamorphosis and heterogamy_, pp. 420-429. Arachnida, pp. 431-455. _Formation of the layers and general development_, pp. 431-446. _Formation of the organs_, pp. 446-455. Formation of the layers and embryonic envelopes in the Tracheata, pp. 456-458. CHAPTER XVIII. CRUSTACEA.