STUDIES ON SEX-DETERMINATION IN AMPHIBIANS. 



37 



lower forms, such as Daphnia and Hydatina. The only experi- 

 ments which have seemed to show that temperature has an influ- 

 ence on sex-determination in the vertebrates are those recently 

 made by Hertwig on Rana. 



In the first experiment which he made to study the influence 

 of temperature on sex-determination Hertwig divided a bunch of 

 eggs of Rana temporaria into two lots ; one lot of eggs was 

 allowed to develop at a temperature of 25 C., the other lot de- 

 veloped at a temperature of 13 C. The mortality among the 

 tadpoles that were subjected to the higher temperature was exceed- 

 ingly great. Out of a total of 200 individuals only 67 under- 

 went metamorphosis, and of this number 4 were males and 63 

 females. The individuals placed in the cold water lived much 

 better that the others, although the development of their genital 

 organs was so greatly retarded that their sex could not be ascer- 

 tained even at the time of metamorphosis. In a second series of 

 experiments on the eggs of Rana esculenta Hertwig obtained the 

 result shown in the following table. 



TABLE III. 



Hertwig considers that the results of these two sets of experi- 

 ments indicate that a high temperature favors the development of 

 females, although he states that a number of individuals in which 

 sex was ascertained is too small to give a decisive answer to the 

 question. In the second experiment the females formed but 34. 1 3 

 per cent, of the individuals that had developed in the warm water 

 and but 16.07 P er cent, of those that had been reared in the cold 

 water. As this experiment stands it hardly seems to me to offer 

 any evidence in support of the view that a high temperature favors 

 the development of females. Both lots of eggs gave a large 

 proportion of males and normally, according to the investigations 

 of von Griesheim ('Si) and of Pfliiger, there appears to be an ex- 

 cess of females among both young and adult frogs. It would 

 be interesting to know under what conditions the eggs used in 



