Heredity and Sex 65 



naturally been drawn that if a means could be devised for 

 increasing the nourishment of the egg or embryo, its develop- 

 ment into a female should be thereby insured, while the 

 reverse treatment should lead to the production of a male. 

 But in practice this a-priori expectation is not fulfilled. 

 Better nourishment of the mother may lead to the produc- 

 tion of more eggs, but not of more female offspring, as has 

 repeatedly been demonstrated by experiment. Also poor 

 nutrition of the mother may diminish the number of eggs 

 which she liberates, but will not increase the proportion 

 of males among the offspring produced. 



An excellent summary of evidence on this point was 

 made by Cuenot in 1900. Attempts to influence the sex 

 of an embryo or larva by altered nutrition of the embryo 

 or larva itself have proved equally futile. Practically the 

 only experimental evidence of value in favor of this idea 

 has been derived from the study of insects, and this is 

 capable of explanation on quite different grounds from 

 those which first suggest themselves. It has sometimes been 

 observed, as by Mary Treat for example, that a lot of insects 

 poorly fed produce an excess of males. In such lots, how- 

 ever, the mortality is commonly high, and more females die 

 than males, because the female is usually larger and requires 

 more food to complete its development. The fallacy in 

 concluding from such evidence that scanty nutrition causes 

 individuals which would otherwise become females to 

 develop into males was indicated years ago by Riley. 

 Nevertheless an argument for the artificial control of sex 

 based on such evidence is from time to time brought forward, 

 as, for example, a few years since by Schenk. The latest 

 advocate of sex control by artificial means is an Italian, 

 Russo (1909). He claims in the case of rabbits that by 



