External Factors of Sex Determination 381 



Thus while poor nourishment increases ihe percentage of 

 males, good nourishment does not increase the percentage of 

 females above the normal. The results may be due, Pictet 

 admits, to mortality rather than to a change in sex affected by 

 the food. 



A number of experiments have been carried out with tadpoles 

 of frogs. An observation made by Born seemed to him to 

 show that the sex of the tadpole of the frog is determined by the 

 amount or by the kind of food eaten by the young animal. He 

 found that when the tadpoles of Rana temporaria (from 

 eggs artificially fertilized) were fed on a mixed vegetable and 

 meat diet, that 95 per cent of them were females and 5 per cent 

 were males. This was a general result obtained from several 

 lots of 1443 tadpoles in all. In some aquaria all the indi- 

 viduals were females. 



The experiments of Yung (1883) are more discriminating. 

 He fed tadpoles of Rana esculenta on different kinds of food. 

 In one lot (A) the flesh of fish was given. These tadpoles were 

 large and well developed. In another lot (B) the flesh of beef 

 and of fish was used. These tadpoles were also large. . In a 

 third lot (C) the white of eggs was used. These tadpoles were 

 smaller. In a fourth lot (D) the yolk of hen's egg was given. 

 These tadpoles were even smaller than the last. The number 

 of males and females that developed is shown in the following 

 table : 



There are also a few other statements by other authors in 

 regard to the influence of food. Thus Balbiani and Henneguy 

 state that an excess of females is found in tadpoles fed on yolk 



