Localization of the Nemertine Egg. 297 



Fig. I. 



Early Cleavage of Entire Egg of Cerebratultis marginatv^. 



A. two-cell stage; side view. B, four-cell stage; side view just after the 

 completion of the second cleavage. C, four-cell stage; from upper pole, slightly 

 later than B. D, eight-cell stage; from lower pole. E, eight-cell stage; side 

 view; the relations of the larger upper quartet to the smaller basal quartet are 

 shown in D and E. F, sixteen-cell stage; side view; the outline of a quadrant 

 is indicated by the heavier line. G, twenty-eight-cell stage; side view, slightly 

 from above; the first break in the rhythm of division is shown in the lagging 

 behind in each quadrant of the cell of the intermediate group which had been 

 derived from the basal cell of that quadrant. H, twenty-eight-cell stage; from 

 lower pole. 



(The present figures, as well as all the following ones, unless otherwise 

 described, were drawn from preparations with the aid of the camera lucida.) 



