666 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



becomes oocyte. The data give no evidence for or against predetermina- 

 tion of the region of the oocyte which protrudes from the chain. Appar- 



FlG. 2i6, A-F. — Association of oocytes and nurse cells in certain annelids. A, B, early and 

 late stage of oocyte development in Ophryoirocha puerilis (after Braem, 1894); C, D, E, early, 

 more advanced, and late stages of oocyte and accessory cells of Diopatra (after Liever, 193 1); 

 F, eight-cell group (one oocyte, seven accessory cells) of To7ttopteris (after Chun, 1888). 



ently it may be on the convex side of a sUght curvature or be determined 

 by mechanical relations between the cells. If this is the case, direction 

 of the polar axis in the oocyte is a matter of chance. Two oocytes occa- 

 sionally develop in a chain but are separated by a number of nutritive 



