TABLE OF CONTENTS. 



Introduction, pp. 1 — 3. 

 Genebative Organs, pp. 3—6. 



CHAPTER I. 



The general development of the Embryo, pp. 7 — 17. 



The fertilised ovum, 7. Tlie segmentation, 8. The formation of the 

 gastrula, 10. General features of the embryo at successive stages, 11. 



CHAPTER II. 



The segmentation of the ovum and the formation of the layers. 



pp. 18—50. 



Structiire of ovum, 18. Ovum of P. Novce-Zealandice and of West- 

 Indian species, 19. Ovum before conjugation of male and female pro- 

 nuclei, 20. The polar bodies, 20. Ovum after conjugation of male 

 and female pronuclei, 21. Structure of segmenting ovum, 21. Syn- 

 cytial nature of the embryo, 24. Primary absence of nuclei in the 

 endoderm and their probable origin, 26. Origin of the enteric space, 27. 

 The nucleus of the fertilised ovum, 28 ; its relation to the extra-nuclear 

 protoplasm, 32. The male and female pronuclei and formation of polar 

 bodies, 33. The nuclei of the ectoderm and of the endoderm, 35. 

 Significance of nuclei, 35. The structure of the gastrula, 37. The 

 polar area, 38. The primitive streak and formation of the mesoderm, 39. 

 Summary and general conclusions, 41. Continuity between the nuclear 

 and extra-nuclear reticula, 43. Continuity of animal cells, 47. 



CHAPTER III. 



The changes from stage A to stage F. pp. 52 — 72. 



The ectoderm, 52. The dorsal hump, 54. The central nervous 

 system, 56. The ventral organs, 59. The cerebral ganglia, 59. Con- 



