THE FACTORS WHICH DETERMINE SEX 625 



Yung l and certain other investigators, have adduced evidence in 

 support of the view that the sex is determined by the quantity 

 and quality of the food supply. Thus they claimed that they 

 could produce an excess of females by feeding the tadpoles upon 

 a meat or fish diet. The conclusions of these authors, however, 

 are hardly borne out by more recent researches, for Cuenot's 

 experiments, 2 conducted on similar lines to those of Born and 

 Yung, show a preponderance of males among tadpoles which 

 were fed upon animal food, and an approximate numerical 

 equality among those which received an exclusively vegetable 

 diet. Moreover, the method adopted by Born for ascertaining 

 the sex of the individual tadpoles during the period of meta- 

 morphosis seems to have been unsatisfactory, since it was based 

 on the assumption that the ovary is always larger than the 

 testicle, whereas this is not invariably the case. It is stated 

 also that frogs' eggs from certain localities yield a higher per- 

 centage of females than those from other localities, and conse- 

 quently that a disproportion of the sexes may exist under normal 

 conditions, but this fact in itself does not show that sex is not 

 determined by nutritive or other environmental influences, but 

 may point to a directly opposite conclusion. But, as Morgan 

 points out, if the natural disproportion between the two sexes 

 is great, errors may easily creep into the experimental results. 3 

 Lastly, King's observations relating to sex-determination in 

 Amphibians provide no evidence that either food or temperature 

 are factors in this process. 4 



The experiments of Treat 5 and other observers who at- 

 tempted to show that the sex of caterpillars could be determined 

 artificially by regulating the supply of food may be disregarded, 

 since it has since been shown that the sex in those animals 

 is already established at the time of hatching, while it is 



1 Yung, "De 1'Influence de la Nature des Aliments sur la Sexualite"," 

 C. R. de VAcad. des Sciences., vol. xciii., 1881. 



2 Cue'not, " Sur la Determination du Sexe chez les Animaux," Bull, Sci. de 

 France et Belg., vol. xxxii., 1899. 



3 Morgan, loc. cit. 



4 King, "Food as a Factor in the Determination of Sex in Amphibians," 

 Biol. Bull., vol. xvi., 1909. "Temperature as a Factor," &c., fiiol. Hull., 

 vol. xviii., 1910. 



5 Treat, " Controlling Sex in Butterflies," American Naturalist, vol. 

 vii., 1873. 



2R 



