22 



Edmund B. Wilson. 



larger than the others. Correlated with this is the fact that these 

 embryos show no lower white area, all the basal quadrants being 

 uniformly pigmented over the lower pole (Figs. 23, 24), which 

 sometimes shows a large opening into the cleavage-cavity (Fig. 



Fig. IV. 

 Cleavage after Removal of the Polar Lobe. 

 20, Two-cell stage and polar lobe after removal of the latter ; 21, four- 

 cell stage of same, from upper pole ; 22, eight-cell stage of same, from upper 

 pole ; 23, sixteen-cell stage of lobeless embryo from lower pole , symmetrical 

 second quartet; 24, similar view of the same stage, open type; 25, sixteen-cell 

 stage, from upper pole ; 26, lobeless embryo from lower pole, after formation 

 of the third quartet; 27, second cleavage, from the side, of egg from which 

 about three- fourths of the first polar lobe had been removed ; 28, a similar 

 form, viewed from the lower pole, after removal of about one-half of the first 

 lobe. 



