Vol. XVI. January, /pop. No. 2 



BIOLOGICAL BULLETIN 



STUDIES ON SEX-DETERMINATION IN 

 AMPHIBIANS. II. 



HELEN DEAN KING. 



It is still an open question whether external factors have any 

 influence on the determination of sex. Much of the experimental 

 work that has seemed to show that sex can be influenced by nu- 

 trition, temperature, etc., has either been carried out with too 

 small a number of individuals or the methods used in the experi- 

 ments have been too crude to give results that could be consid- 

 ered as decisive. It is seemingly quite within the power of the 

 modern investigator to determine definitely whether sex can be 

 influenced by external factors ; and careful work, such as that 

 which has been done by Cuenot and Hertwig, should settle this 

 question for all time. If it is found that external factors do in- 

 fluence sex then the current chromosome-sex theory will have to be 

 abandoned or considerably modified ; if, on the other hand, it is 

 shown convincingly that external factors have no influence on sex- 

 determination, then the way is cleared for the theory that best 

 explains the facts known to us and offers the most favorable 

 hypothesis for future investigations along this line. 



Several years ago I started a series of experiments on the eggs 

 of the common American toad, Biifo lentiginosus, in order to 

 study the problem of sex-determination in this amphibian which 

 seems to furnish peculiarly favorable material for an investigation 

 of this kind. In the first experiments that were made the influ- 

 ence of nutrition on the determination of sex was investigated. 

 The results of this work, as shown in a previous paper (King, '07), 

 seem to indicate that neither the quantity nor the quality of the 

 food given the larvae has any influence on sex. The present 

 paper records the results of the second series of experiments that 



27 



