624 WILSON. 



PLATE XXXI. 



[All from preparations ; 270 diameters.] 



Fig. 25. Fourth cleavage, strict bilateral form /, upper pole. 



Figs. 26-28. i6-celled stage, bilateral form /; the same specimen shown from 

 upper pole, lower pole, and from the side. 



Fig. 29. The same specimen as Fig. 22, from lower pole, showmg cleavage- 

 pore. 



Fig. 30. Bilateral form /, from lower pole ; large cleavage-pore. 



Figs. 31-32. Strict spiral form, i6-celled stage ; the same specimen from op- 

 posite poles. Cell-connections hypothetical. 



Figs. 33-34. Fifth cleavage, nearly pure bilateral form /; 33 from lower pole, 

 34 from side. Origin of second group of micromeres. 



Figs. 35-36. Fifth cleavage, bilateral form /; 35 from side, 36 from upper 

 pole. Note asymmetry of spindle in x. 



