100 SEX 



that some animals produce two kinds of ova, 

 e. g. large and small, and that the larger 

 develop into females. This may be illus- 

 trated by Hydatina senta among Rotifers; 

 the large eggs develop into females, the small 

 ones into males. 



(c) Some conclusions as to the determina- 

 tion of the sex of the offspring have been 

 based on experiment, e. g. subjecting the eggs, 

 or the embryos, or the parents, to peculiar 

 conditions of nutrition, temperature, and the 

 like, and observing whether the numerical 

 proportion of the sexes in the offspring is in 

 any way different from that which obtains 

 in ordinary conditions ; or by contrasting the 

 results of fertilising immature and over-ripe 

 ova; or by contrasting the results of using 

 fresh or stale sperms ; or by trying particular 

 breeding experiments in reference to what are 

 called sex-limited characters. 



POSSIBLE INFLUENCE OF ENVIRONMENT ON 

 DEVELOPING ORGANISM. The first theory 

 we shall notice lays emphasis on " Nurture " 

 in the wide sense. It supposes that in some 

 cases the sex of the offspring remains un- 

 determined for a considerable time, and that 

 environmental conditions nutritive in par- 

 ticular give the bias to one side or the 

 other. Yung, of Geneva, who was one of the 

 first to attempt the experimental study of 

 sex-determination, found that tadpoles, which 

 normally develop into about fifty-seven 

 females to forty-three males, yielded, when 

 fed with beef, fish and frog-flesh, respectively, 

 seventy-eight, eighty-one, and ninety-two 

 females in the hundred. But Yung did not 



