MATURATION, 



17 



In Ascaris, whose diploid number of chromosomes is four, both maturation 

 divisions occur after the sperm has entered the egg and lies embedded there 



FIG. 10. Maturation of the ovum of Ascaris megalocephala (bivalens). Boveri, Wilson. A, 

 The ovum with the spermatozoon just entering at x" ', the egg nucleus contains 2 tetrads 

 (one not clearly shown), the somatic number of chromosomes being 4. B, Tetrads in pro- 

 file. C, Tetrads on end. D, E, first spindle forming. F, Tetrads dividing. G, First polar 

 body formed, containing 2 dyads; 2 dyads left in the ovum. H, /, Dyads rotating in pre- 

 paration for next division. /, Dyads dividing. K, Each dyad divided into 2 single chro- 

 mosomes, thus completing the reduction. 



as the male pronucleus. An achromatic spindle forms near the surface of 

 the ovum and the two tetrads go to the equatorial plane (Fig. 10, E). Each 



