226 HELEN DEAN KING. 



water. The rather unusual sex ratios obtained in the acid series 

 would be explained, on this assumption, as due either to chance 

 or to the action of the solution on the spermatozoa. There is, 

 however, another possible explanation that would serve to bring 

 these results in line with those obtained by subjecting eggs to 

 conditions which tend to lessen the water contents during the 

 fertilization period. It is known that egg membranes are more 

 readily permeable to weak acid than to weak alkaline solutions, 

 and as the jelly-like mass that surrounds the unfertilized eggs of 

 Bufo is relatively thick, as is also the zona pellucida that incloses 

 each individual egg, it is possible that in these experiments only 

 the acid solutions were able to penetrate the membranes and 

 act on the eggs. That this interpretation of the results is at 

 least plausible is indicated from the sex ratios obtained in the 

 series of experiments about to be described where fertilizing eggs 

 in acid solutions again leads to a seeming increase in the relative 

 proportion of males, while practically normal sex ratios are 

 found where the eggs were fertilized in solutions of NaOH. 



In a former study of the effects of temperature on the deter- 

 mination of sex on Bufo (King, '10), the results obtained seemed 

 to indicate the possibility that temperature, acting at the time 

 of fertilization, might indirectly influence the sex-determining 

 process; a high temperature favoring the development of females, 

 a low temperature tending to the production of relatively more 

 males. These experiments showed, however, that the temper- 

 ature at which the eggs are fertilized cannot be the dominating 

 factor in determining sex in Bufo, and that at most its influence 

 would be to facilitate or to hinder certain processes taking place 

 in the egg that are concerned with sex-determination. 



In the experiments just described the various lots of eggs 

 were fertilized in solutions that were kept at room temperature 

 (20 C.) during the time that they were allowed to act on the eggs. 

 In another series of experiments a batch of eggs from the female 

 whose eggs were used for the alcohol series of experiments (Table 

 I.) was divided into lots of several hundred eggs each. Each 

 lot of eggs was then fertilized with spermatozoa from the same male 

 in a .0050 per cent, solution of acetic acid or of sodium hydrate 

 that was kept at a temperature of 28, 20 or 11 C. during the 



