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CLAUDE W. MITCHELL 



either the majority of individuals were of the saccate type, or 

 the slow rate of reproduction indicated that the individuals, 

 though humped, were not of a high physiological potential, or 

 the general food supply had been inadequate. 



So extreme was the male production in the mass cultures 

 indicated above that a few of the smaller ones were examined, 

 individual by individual, with the microscope. The percentage 

 of male producers is given in table 9. It will be seen that in 

 one case the number of male producers simultaneously present 

 reached the surprising maximum of 92 per cent of the entire 

 culture. 



TABLE 9 . . 



Starvation of mass cultures of humped individuals 



GENERAL DISCUSSION OF LITERATURE 



In thus reaching the conclusions that male production — hence 

 sex-determination — in Asplanchna is a phenomenon all but 

 wholly under nutritive control, it naturally becomes incumbent 

 to consider briefly the discrepancy between this conclusion and 

 the results which have been reached by others. 



There is of course, first of all, the possibility that nutrition 

 is a more important factor of sex control in Asplanchna than 

 even in other genera of rotifers. But it seems more probable that 

 its role is the same in all with the exception of the fact that the 

 enormous nutritional irregularities natural to Asplanchna enable 

 one to produce results which in degree of definiteness and contrast 

 m.ay well exceed those producible in Hydatina. We ascribe, thus, 

 much of our success to the choice of a species favorable for ex- 

 perimental work. 



