STUDIES ON SEX-DETERMINATION IN AMPHIBIANS. 23! 



ments described in this paper that makes it impossible to draw 

 any positive conclusions from the results obtained, however defi- 

 nite they may appear in some cases. The mortality in the various 

 lots of individuals was very great and only a small percentage of 

 the eggs with which any experiment was started were carried 

 through to metamorphosis and their sex ascertained. The possi- 

 bility exists, therefore, that the results may be due solely to chance 

 or to selective mortality, and that in no case was the normal sex 

 ratio really changed by subjecting eggs to the influence of various 

 external factors at or before the time of fertilization. There is, how- 

 ever, no evident relation between mortality and sex in tadpoles 

 reared under artificial conditions, as shown by the investigations 

 of Pfliiger ('82) and also by my former work. It does not seem 

 probable, therefore, that in certain lots subjected to similar treat- 

 ment at the time of fertilization more males than females would 

 always die; while in other lots, where the eggs had received dif- 

 ferent treatment, the mortality would invariably be greater among 

 the females. Practically normal sex ratios were obtained in all 

 of the control experiments, in the alcohol series, and also in that 

 in which lots of eggs from the same female were fertilized with 

 spermatozoa from different males. This uniformity in the re- 

 sults of so many series of experiments makes it even more im- 

 probable that mortality was selective in other cases ; neither does 

 it seems possible that the unusual sex ratios obtained in some 

 instances could be chance variations. 



The results of the various experiments in which eggs were 

 fertilized in solutions of acetic acid are so uniform that they 

 seem to me very suggestive, even if no definite conclusions from 

 them are possible. Altogether a total of seven lots of eggs from 

 four different females were fertilized in acid solutions. In every 

 instance the percentage of females that was obtained was from 

 10-20 per cent, lower than that which is probably normal for 

 the species. There is apparently something in this series that 

 stands for a tendency to the production of males rather than of 

 females. These results taken in connection with the equally 

 clear-cut results that were obtained in the five experiments in 

 which water was extracted from the egg, or the egg prevented 

 from absorbing water, would seem to indicate that the relative 



