126 THE MENDEL JOURNAL 



individuals. It was assumed that if we knew 

 these conditions we should be able to decide at 

 will the sex of the unborn young. Acting under the 

 influence of such a belief, several investigators 

 designed and carried into operation various experi- 

 ments that were intended to show the part which 

 different factors in the environment played in the 

 determination of sex. The well-known experiment 

 of Yung with tadpoles was of this class. In 

 this experiment, certain tadpoles were fed on very 

 nutritive and abundant food, while others were 

 fed on less nutritive and limited material. It 

 was found that there was a larger percentage of 

 female frogs derived from the former and of male 

 frogs from the latter. The conclusion thus suggested 

 itself that females were determined by excessive 

 anabolic or building up process of nutrition, and 

 males by that antithetic process in which anabolism 

 only just keeps in excess of the katabolic or breaking 

 down processes. But there were several sources 

 of error in such an experiment. The most serious 

 one is indicated by a similar experiment with the 

 caterpillars of certain butterflies. In this experiment 

 it was ascertained that under-feeding did not result 

 in the production of an excess of males, but in the 

 elimination of the females. There being a heavy 

 mortality among the females, it is a natural con- 

 sequence that there appears to be an excess of 

 males. But it is apparent and not real. ■ It is, 

 therefore, in reality, not a case of sex- determination 

 by environmental influences, but one of survival 



