PARTHENOGENESIS 



177 



produces eggs, all of which give rise to females or else 

 to males. In connection with this fact he finds that 

 the eggs of some females do not give off any polar 

 bodies but retain the full number (20) of chromosomes. 



m 



if? 



D 





Fig. 91. — Illustrating chromosome cycle in Neuroterus. A, one type of 

 spring female, whose eggs (containing 20 chromosomes) produce no polar 

 bodies. Only sexual females result. B, the other type of spring female 

 whose eggs form two polar bodies, leaving 10 chromosomes in egg. These 

 eggs give rise to males. C, ripening of egg of sexual female (2d generation), 

 and D, spermatogenesis of male (second generation). 



These eggs produce sexual females (in left-hand side 

 of Fig. 91). From the eggs of other parthenogenetic fe- 

 males two polar bodies are given off, and the half (10) 

 number of chromosomes is left in the egg (see right-hand 

 side of Fig. 91). These eggs produce males. The life 



