284 



CELL-DIVISIOX AND DEVELOPMENT 



result, and concluded that even when the ^^g approaches the 

 spherical form the symmetry still exists, though obscured. More- 

 over, according to Hallez ('86) and later writers, the egg always lies 

 in the same position in the oviduct, its cephalic end being turned 



a 



\ 



B 



C 



Fig. 129. — Eggs of the insect Corixa. [Metschnikoff.] 

 A. Early stage before formation of tlie embryo, from one side. B. The same viewed in the 

 plane of svmmetrv. C. The embryo in its final position. 



a, anterior end; /, posterior; /, left side, ;-, right; v, ventral, d, dorsal aspect. (These letters 

 refer' to the final position of the embryo, which is nearly diametrically opposite to that in which it 

 first develops) ; m, micropyle ; near/ is the pedicle by which the egg is attached. 



forwards towards the upper end of the oviduct, and hence towards 

 the head-end of the mother.^ 



1 The micropyle usually lies at or near the anterior end, but may be at the posterior. 

 It is a very important fact that the position of the polar bodies varies, being sometimes at 

 the anterior end, sometimes on the side, either dorsal or lateral (Heider, Blochmann). 



