THE INFLUENCE OF FOOD IN CONTROLLING SEX 

 IN HYDATINA SENTA 



DAVID DAY WHITNEY 



From the Biological Laboratoi-y, Wcsleyan University 



Considerable interest has been manifested concerning the sex 

 ratio in the parthenogenetically produced male and female 

 individuals in the rotifer Hydatina senta. At one time in general 

 cultures of rotifers only females are found, at another time fe- 

 males and males are found in equal numbers, and at still other 

 times very few females but from 80 to 90 per cent of males are 

 found. 



The problem has been to determine the causes that regulate 

 the production of the two sexes in this rotifer — why at one time 

 there is produced an excess of females and at another time an 

 excess of males. 



The results of the work of earlier investigators on this problem 

 having been reviewed so thoroughly and frequently recently, 

 only references to them in the bibliography will be made at this 

 time. 



Whitney made an extensive series of experiments and obser- 

 vations in regard to temperature and starvation and came to 

 the conclusion that neither factor was influential in the regu- 

 lation of the production of the two sexes. He, moreover, found 

 that the so-called female sex strains of Punnett could be made 

 to produce many males by changing the environment. How- 

 ever, he was unable to discover the real factor that changed the 

 female sex strain into one that produced many males, but he was 

 of the opinion that whatever the potent factor was that some- 

 times caused only females to be produced and at other times 

 caused nearly all males to be produced, it must be an external 

 factor. Moreover, he made observations on one strain through 

 289 generations, for about two years, in which no males were 



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