FOOD AS A FACTOR IN THE DETERMINATION OF SEX. 47 



500 individuals were collected one morning from the bank of the 

 Susquehanna River at Owego, N. Y., during the latter part of 

 June, 1904. The sex of each individual was ascertained by the 

 method described above, it being necessary to make a histological 

 examination of the gonads in only about twenty cases. The 

 result of the investigation is summarized by hundreds in the fol- 

 lowing table. 



Table I. 



Number of Individuals. Males. Females. 



100 SI 49 



100 44 56 



100 46 54 



100 48 52 



100 52 48 



500 241 259 



Of the total of 500 individuals, 259 or 51.8 per cent, were 

 females, and 241 or 48.2 per cent, were males. In Bttfo the 

 excess of females among the young seems to be somewhat less 

 than that among young frogs, as according to an investigation 

 made by von Griesheim of the sex of 440 young Ranafitsca, 280 

 or 63.7 per cent, were females. 



Although in the adult state the female toad is noticeably larger 

 than the male, it is not possible to distinguish the sex of very 

 young toads by their size alone. Two hundred individuals in this 

 group were sorted according to size and it was found that, in many 

 cases, the larger individuals were males. Any variation that may 

 exist in the size of the individuals at the time of metamorphosis 

 can probably be attributed to the difference in the amount of food 

 that the tadpoles were able to obtain. 



Experiments. 



If food is a decisive factor in sex determination, it may be 

 considered to act in one of two ways : either through the quantity 

 of nourishment that it affords the organism ; or through its par- 

 ticular chemical nature as a proteid, a hydrocarbon, etc. An 

 abundant nutrition is held by many investigators to lead to the 

 development of an excess of females ; while, on the other hand, 

 scarcity of food, according to Schenk (10) and others, tends to 



