MATURATION 



145 



FIG. 77. Maturation in the egg of Ascaris megalocephala bivalens. From 

 Wilson, "Cell," after Boveri. A. Egg with spermatozoon just entering at d\ 

 The germinal vesicle contains two rod-shaped tetrads (only one clearly shown). 

 B, C. Tetrads seen in profile and end views. D. First polar spindle forming (in 

 this case within the germinal vesicle). E. First polar spindle in definitive posi- 

 tion. F. Tetrads dividing. G. First polar body formed, containing, like the 

 egg, two dyads. H, I. Dyads rotating into position for the second division. 

 /. Dyads dividing. K. Each dyad has divided into two single chromosomes, 

 as the second polar division approaches. (For final stages, see Fig. 94.) 



