STUDIES ON SEX-DETERMINATION IN AMPHIBIANS. 



227 



half hour that the eggs remained in it. It was hoped that 

 by this means more certain evidence of the action of temperature 

 in determining sex in Bufo might be obtained, since a high tem- 

 perature would probably facilitate the penetration of a solution 

 into the egg and a low temperature would tend to retard it. 

 Any change in the sex ratio greater than that shown in the other 

 series of experiments in which eggs were fertilized in acid or in 

 alkaline solutions might therefore be attributed to the effects 

 of the temperature at which the solution acted. 



A small proportion only of the eggs that were used in these 

 various experiments segmented; and, as in other experiments 

 in which eggs were subjected to abnormal conditions at the time 

 of fertilization, many of the tadpoles died during the early 

 growth period. The results obtained in the acid series are 

 brought together in Table VIII.; the percentage of females given 

 as a control being the same as that for the alcohol series (Table I.). 



TABLE VIII. 

 EGGS FERTILIZED IN ACID SOLUTIONS AT DIFFERENT TEMPERATURES. 



In spite of the comparatively small number of individuals 

 in which sex was ascertained, very uniform sex ratios were found 

 in all the various lots, and in every case the percentage of females 

 falls far below that which is apparently normal for the species. 

 The smallest proportion of females was found in the lot in w r hich 

 the eggs had been fertilized at the highest temperature; and, 

 conversely, the greatest number of females appears where fertili- 

 zation was effected at a temperature of nC. This is the result 

 one would expect if the higher temperature had facilitated the 

 penetration ityto the egg of a solution that could influence the 

 sex-determining mechanism in such a w r ay as to increase its 

 tendency to produce a male. The difference between the per- 

 centages of females in the two lots in which the eggs were fertil- 



