EXTRAOVATE EXPERIMENTS. 



215 



Experiments on the Egg of Arbacia. 



In eight eggs with an extraovatc, cleavage was followed up to 

 the formation of the micromeres. Of these, four segmented normally 

 (Figs. I and 2), while the rest showed some deviations from the nor- 

 mal mode of cleavage. The difference in size of extraovate cannot be 

 taken as the cause of abnormal cleavage, since an egg with a large 

 extraovate was divided normally. It should be remarked that in ab- 

 normally cleaved eggs their abnormality lies always near the region 

 where the extraovatc is attached (Figs. 3, 4 and 5). 



Figs. 6-8. Early cleavage stages of Sirongylocentrotits egg with an extraovate. 



