42 HELEN DEAN KING. 



The sex ratio found among the individuals in Lot D, agreeing 

 with that of Lot B, shows a considerable deviation from the sex 

 ratio that is presumably normal for the species. In a total of 

 2,083 individuals which developed from eggs laid in water with 

 a temperature of 9 C. there were 902 or 43.30 per cent, of 

 females. Only once in the course of my investigations on sex- 

 determination in Bnfo have I found the proportion of females in 

 a lot of individuals anywhere near as low as that found in Lots 

 B and D in the above experiments. In studying the influence 

 of nutrition on sex-determination in Bufo I found that in a total 

 of 349 individuals that had been fed on mixed animal and vege- 

 table food only 45.84 per cent, were females. Other lots of eggs 

 laid by the same females gave as high as 59 per cent, of females 

 however ; and on summarizing the results obtained in the entire 

 series of experiments it was found that the females formed 53.58 

 per cent, of the total number of individuals in which sex was 

 ascertained. In the last experiment described there were 2,127 

 or 49. 9 1 per cent, of females among the 4,261 individuals whose 

 sex was ascertained. This fact strongly suggests that the sex 

 ratio in this lot of individuals was affected by the conditions under 

 which the eggs were laid. 



The results of the experiments described in this section indi- 

 cate, although they by no means prove, that the temperature of 

 the water in which the eggs are fertilized has some influence on 

 the determination of sex in Bnfo. A high temperature appears 

 to favor the development of females ; a low temperature, on the 

 other hand, seems to lead to the development of relatively more 

 males. It is possible, as before suggested, that the results ob- 

 tained in these experiments may be due to the fact that the sex 

 ratio in Bufo is a variable one, the proportion of females ranging 

 from 35-70 per cent, in lots of eggs laid by different females. 

 If such is the case it surely is a strange coincidence that lots of 

 eggs should have' been taken for these temperature experiments 

 which would give the greatest extremes in the sex ratio. 



One serious objection that can be made to these experiments 

 is that the eggs which were fertilized in warm water were laid by 

 one female while the eggs fertilized in the cold water were laid 

 by another individual. This gives an opportunity for the results 



