650 THE PHYSIOLOGY OF REPRODUCTION 



and consequently he is inclined to believe ttat in man, at 

 any rate, the determination of sex is independent of parental 

 nutrition. In any case its influence can be but small." 



Cuenot's experiments ^ upon rats, in which some were fed 

 mainly on bread and others were fed upon an abundant supply 

 of difierent kinds of food, yielded no evidence of a preponderance 

 of one sex among the better-nourished individuals. 



Lastly, in Schultze's experiments ^ on mice, in which one 

 lot was starved and other lots were variously nourished upon 

 different kinds of foods, there is no evidence that sex-determina- 

 tion is regulated by nutrition. 



Schultze and Morgan conclude that if nutrition really in- 

 fluences the proportion of the sexes, it is probable that it does 

 so indirectly by ehminating one or the other kind of egg. This 

 suggestion has been further elaborated by Heape, as described 

 above (p. 641). 



Newcomb's Statistical Investigation. — ^Newcomb,^ as a result 

 of an investigation into the statistics of multiple births, has 

 come to the conclusion that sex is estabhshed at different periods 

 of development in different cases. He shows that there is a 

 tendency among human offspring for twins to be of the same 

 sex, a fact which he regards as supplying a " practically con- 

 clusive negation of the theory of completely determined sex in 

 the original germs." His conclusion appears to be that sex 

 is estabhshed by " accidental causes," the nature of which is 

 at present unknown, and that in the case of twins the sex- 

 determining factors act similarly on both children, and so tend 

 towards a uniformity of sex. But he omits to mention the 

 probabiUty that some twin embryos arise from a single ovum, 

 a fact which would account for their sexual identity on the 

 assumption that sex is already determined in the germ cell. 



Hekmaphroditism and Sexual Latency 



Organisms which combine within themselves the essential 

 characters of both sexes are said to be hermaphrodite. True 

 hermaphrodites produce both ova and spermatozoa, but there 



1 Cuenot, loc. cit. ' Schultze, he. cit. 



' Newcomb, loc. cit. 



