92 LILLIE. 



EXPLANATION OF PLATE II. 



Fig. i6. Eight-cell stage from the right side. Lower pole rolled up a little. 



Fig. 17. Passage to nine-cell stage from behind. Formation of first somato- 

 blast, d^ = X. 



Fig. 18. Anterior view of the same egg. 



Fig. 19. Ten-cell stage from the right side. Formation of the second gener- 

 ation of ectomeres. 



Fig. 20. Thirteen-cell stage from the upper pole. </' of the first generation 

 of ectomeres has divided. The large cells of the second row are the members of 

 the second generation of ectomeres. 



Fig. 21. The same egg from the right side, showing the arrangement of the 

 macromeres also. 



Fig. 22. Seventeen-cell stage from the upper pole. All of the first generation 

 of ectomeres have divided, x^ is the seventeenth cell. 



Fig. 23. The same egg from the vegetative pole. The spindle in Z> is for the 

 separation of ^3 to the left. 



Fig. 24. Eighteen-cell stage from the upper pole and partly from in front. 

 Spindles inaz, b^ , c^, and d^ (cf. Fig. 25). 



Fig. 25. The same egg from the left side. The spindle in a 2 separates a 22 — 

 the larval mesoblast. 



Fig. 26. Eighteen-cell stage directly from above. 



Fig. 27. The same egg from the lower pole. 



