The Cellular Basis 167 



cent of male offspring. Many earlier investigators had found that 

 food influences sex, though usually it was held that scanty food led 

 to the production of males and abundant food to females, but this 

 older work, unlike Whitney's, was generally uncritical. A. F. 

 Shull finds that "the irrevocable event leading to the determination 

 of the sex of any given parthenogenetically produced individual 

 (rotifer) occurs in the maturation of the egg from which that in- 

 dividual's mother develops .... Probably a definite chemical 

 change in the proteins of the chromosomes occurs at the time of 

 maturation." The diet may thus affect the chromosomes and 

 through these the sex. 



Extensive statistics show that in many animals including man 

 more males are born than females, whereas according to the chro- 

 mosome theory of sex-determination as many female-producing 

 spermatozoa are formed as male-producing ones. It is possible 

 to explain such departure from the I : i ratio of males to fe- 

 males in conformity with the chromosome theory if one class of 

 spermatozoa are more active or have greater vitality than the 

 other class, or if after fertilization one sex is more likely to live 

 than the other. In the human species it is known that mortality 

 is greater in male babies before and after birth than in female 

 babies, but if before fertilization the activity or vitality of male- 

 producing spermatozoa is greater than that of female-producing 

 ones it would offer a possible explanation of the greater number of 

 males than of females at the time of birth. In certain insects it is 

 known that only females develop from fertilized eggs, and in 

 one of these cases, viz., Phylloxera, Morgan has discovered that 

 this is due to the fact that all the male-producing spermatozoa 

 degenerate and that only female-producing spermatozoa become 

 functional. Possibly experimental alterations of the sex ratio, 

 such as Hertwig, King, Whitney and others have brought about 

 may be explained as due to a differential action of the modified 

 egg cells or of the environment upon the two types of sperma- 

 tozoa. In the Drosophila work many lethal mutations have ap- 



