98 



SEX INHERITANCE 



An environmental change determines whether par- 

 thenogenesis or sexual reproduction takes place. 

 The environment may equally well be said to de- 



Hydat/na senta 





yi^/7iy. o. 



.'^fllffif c. 



///ll^i . tf- /■'■' t/"t^> > 



^nafc 



Fig. 33. — Diagram to illustrate the life cycle of Hydatina senta. The 

 environment determines whether the parthenogenetic individual (at the 

 top) gives rise to a female like herself , or to one that if fertilized at an 

 early age produces a sexual egg, but if not fertihzed produces small eggs 

 from which males develop parthenogenetically. 



termine whether an egg becomes a parthenogenetic 

 female-producing female or a male-producing female. 



