GENERAL OUTLINE 



239 



eight somatic chromosomes — the highest number thus far accurately 

 counted. As the first polar body forms, each of the tetrads is halved 

 to form two double groups, or dyads, one of which remains in the Q.g^ 



B 



C 





F 



"^ '■ )mmm^^ 



I 



K 



Fig. 117. — Formation of the polar bodies in Ascaris megalocephala, van bivalens. [BOVERI.] 

 A. The egg with the spermatozoon just entering at S ; the germinal vesicle contains two rod- 

 shaped tetrads (only one clearly shown), the number of chromosomes in earlier divisions having 

 been four. B. The tetrads seen in profile. C. The same in end view. D. First spindle forming 

 (in this case inside the germinal vesicle). E. First polar spindle. F. The tetrads dividing. 

 G. First polar body formed, containing, like the egg, two dyads. H. I. The dyads rotating into 

 position for the second division. J. The dyads dividing. K. Each dyad has divided into two 

 single chromosomes, completing the reduction. (For later stages see Fig. 90.) 



