186 



PHYSICAL BASIS OF HEEEDITY 



for, owing to the few sperms produced by each male their 

 actual number can be counted. There are twice as many 

 large as small spemiatozoa, if, as may be the case, only 

 the large ones contain chromosomes and are functional, 



Fig. 85. — Hydatina senta, adult female, A; young female soon after hatching, B; adult 

 male, C; parthenogenetic egg, D; male-producing egg, E; resting egg, F. (After Whitney.) 



the conditions here would appear to be like those in the 

 hornet, provided there are no chromosomes in the small 

 spermatozoa. This would also explain why all fertilized 

 eggs produce females. 



So long as the ordinary parthenogenetic females are 

 fed on the poor diet of Polytoma, they continue to produce 



