TEMPERATURE AS A FACTOR IN THE DETER- 

 MINATION OF SEX IN AMPHIBIANS. 



HELEN DEAN KING, 

 Assistant in Anatomy at the Wistar Institute. 



In 1905, Hertwig (i) published the results of a series of experi- 

 ments on the eggs of Rana teniporaria and of Rana esailenta 

 which showed, according to his interpretation, that temperature is 

 a sex-determining factor in amphibians : a high temperature 

 favoring the development of females ; a low temperature causing 

 the production of relatively more males. This conclusion is in 

 accord with the results of Issakowitsch's (2) earlier experiments 

 on sex-determination in Daphnia ; but it is opposed by the results 

 of Maupas' (7) experiments on Hydatina senta and by those of 

 von Malsen (6) on Dinopliilus apatris. The latter experiments 

 seemed to indicate that heat leads to the development of males 

 and that cold tends to the production of females. Maupas and 

 Hertwig believe that temperature acts directly on the sex-cells : 

 Issakowitsch and von Malsen, on the other hand, maintain that 

 nutrition is the dominant factor in sex-determination, temperature 

 acting only indirectly through its influence on the processes of 

 assimilation in the parent organism. 



In the spring of 1907, I made a series of temperature experi- 

 ments on the eggs of the toad, Bufo lentiginosus, which were 

 carried out in a manner similar to those made by Hertwig on the 

 eggs of Rana. Various lots of fertilized eggs were placed in 

 tanks in which the water was kept at a nearly constant tempera- 

 ture until the tadpoles underwent metamorphosis (King, 5). In 

 Btifo as in Rana, the sexes cannot be distinguished until the end 

 of metamorphosis unless the gonads are sectioned. It is con- 

 ceivable, therefore, that sex in these forms may not be determined 

 until a relatively late period and that temperature, acting during 

 the entire growth period of the tadpoles, might alter the normal 

 sex-ratio. Two series of experiments were made with eggs from 

 different females. In one series (lot A) 62.5 per cent, of the in- 



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