232 



Edmund B. JVilson. 



fashion, these being likewise composed mainly or wholly of white 

 material (Fig. 87). Beyond this point (16/2 stage) I have not 

 followed the divisions. 



Fig. IX. 



Cleavage of Isolated Blastomercs in Dentalium. 



83, 88. isolated AB and CD halves, before division; 83-87, cleavage of AB- 

 half; 84, 85, 4/2-cell stage, from, the side; 86, 8/2-cell stage, from the side; 87, 

 16/2-cell stage, from the side; 88-93, cleavage of CD-half; 88-90, first cleavage 

 (second polar lobe) and resulting 4/2-cell stage, from the side; 91, second 

 cleavage (third polar lobe) from the side; 92, resulting 8/2-cell stage, oblique 

 view, from the side and above; 93, 16/2-cell stage, with first somatoblast, 2d 

 (X) obliquely from the side; 94, 2-cell stage of C-fourth; 95-99. cleavage of 

 D-fourth; 95, 96, trefoils; 97, 98, 8/4-cell stages; 99, 16/4-cell stage (seen from 

 the inner side, so as to appear reversed). 



