Plate II. 



Fig. 14.— Section through an ovum just laid, x 490. 



Fig. 15. — Second polar mitosis at the metaphase. x 912 (immers). 



Fig. 16. — Same, viewed from a pole, x 912 (immers). 



Fig. 17. — Same, whose figure lies parallel to the surface of the egg. x 800. 



Fig. 18. — Section through an ovum, into which a spermatozoon has entered. 

 x 800. 



Fig. 19. — Section through an ovum, in which the sperm ($)- and egg- 

 nuclei (Ç) are still without their membrane. x 912 (immers). 



Fig. 20. — Egg-nucleus travelling toward the centre of the ovum. A polar 

 body is seen in this section, x 912 (immers). 



Fig. 21. — Sperm and egg nuclei at the centre of the ovum. 912 (immers). 



Fig. 22. — Sperm and egg nuclei fusing. x 500. 



Fig. 23. — Segmentation mitosis in the early prophase, x 912 (immers). 



Fig. 24. — Segmentation mitosis in the early anaphase, x 912 (immers). 



Fig. 25. — Segmentation mitosis in the late anaphase, x 912 (immers). 



Fig. 26. — Section through an egg at the 2-cell stage. x 490. 



Fig. 27.— Section through an egg at the 8-cell stage, x 490. 



Fig. 28. — Portion of a section through an egg at the 8-cell stage, in 

 which the fourth cleavage mitosis has taken place, x 800. 



Fig. 29. — Section through an egg at the 16-cell stage, in which the seg- 

 mentation cavity is seen, x 490. 



Fig. 30. — Section through an egg at nearly the 32-cell stage (slightly 

 departed from the normal cleavage), x 490. 



Fig. 31. — Blastula, from toto preparation (optical section), x 370. 



Fig. 32.— Median section through a blastula. x 490. 



Fi<r. 33. — Median section through an early gastrula. x 500. 



