278 GEO. W. TANNREUTHER. 



Explanation of Plate X. 



Fig. 14. Fourth and fifth cleavages completed ; a, animal ; v, vegetative pole. 



Fig. 17. Blastula with primitive ectoderm cells, just before the formation of the 

 endoderm. 



Fig. 20. Cleavage cavity completely filled with endoderm cells and the begin- 

 ning of the outer egg membrane. 



Figs. 21-26. Formation of the outer and inner egg membranes ; 0, outgrowths. 



Figs. 27-32. Different shapes which the egg assumes in passing to the exterior 

 of the ectoderm. 



