38 RALPH E. WAGER. 



Explanation of Plate IV. 



Fig. 24. Equatorial section through the egg segmented to the eight-celled stage. 

 The cleavage cavity and protoplasmic bridges are well shown. 



Fig. 25. Similar section through the egg at a little later stage. The cleavage 

 cavity is more definite and a variation in the size of the blastomeres is noticeable. 



Fig. 26. Section through the segmented egg at a more advanced stage. In this 

 case the process seems to have been unusually regular. The blastomeres are appar- 

 ently of nearly uniform size, and regularly arranged. 



Fig. 27. Segmentation carried to the completion of the hollow mass of cells just 

 before the beginning of the formation of the primitive entoderm cells. Some of the 

 cells are noticeably larger and longer than others. 



Fig. 28. The growth of the egg completed. The first polar body is to be seen 

 just beneath the ectodermal covering. The egg membrane is also visible as a thin 

 slightly shaded area beneath the ectoderm. 



Fig. 29. The protoplasmic prcicess from the ectodermal cells about which the 

 spiculate structures are formed. The chitinous envelope is already forming. The 

 dark spot in one of the processes is not a pseudo-cell, but a piece of foreign matter in 

 the preparation. 



