276 GEO. W. TANNREUTHER. 



Explanation of Plate IX. 



Fig. 8. Section through the animal pole of egg showing polar bodies with con- 

 nective thread of protoplasm; p.b, polar bodies ; pr.n, pro-nucleus; e.m, egg mem- 

 brane. X 75°- 



Figs. 9 and 10. Sections of eggs passing through poles, showing first cleavage and 

 protoplasmic connections between cleavage cells : p.c, protoplasmic connections. 



Fig. 11. First cleavage completed, and division of nuclei for second cleavage. 



X 55- 



Fig. 12. Section of egg at right angles to polar axis, showing second cleavage 

 complete. X 5^. 



Fig. 13. Section of egg passing through poles with third cleavage completed and 

 beginning of cleavage cavity ; cl.c, cleavage cavity. 



Fig. 15. Fourth and fifth cleavages complete. Cleavage cells becoming flattened 

 out around the cleavage cavity. 



Fig. 16. Stage a little later than preceding. 



Fig. 18. Maximum development of cleavage cavity ; primitive ectoderm cells 

 dividing to form endoderm. 



Fig. 19. Cleavage cavity becoming filled with endodermal cells. 



