260 GENETICS AND EUGENICS 



develop into a female, since Egg 11 + Sperm 11 = 22, the 

 female number. The first man to suggest a relation between 

 the odd chromosome and sex determination (McClung) sup- 

 posed of course that the extra chromosome must go to pro- 

 duce a male, the more important sex, and he called it a male 

 sex-determining chromosome, but it turned out otherwise. The 

 extra chromosome is really a female sex determinant. When 

 a difference exists between the sexes in chromatin content, 

 it is regularly the female that has the larger supply. The 

 significance of this we may inquire into further. 



In some cases, several of which are described by Morgan, 

 the number of chromosomes is found to be the same in both 

 sexes, but one of the chromosomes in the female is regularly 

 larger than the corresponding chromosome in the male. This 

 indicates that the female, in this case also, contains some 

 chromosome element not found in the other sex. 



But Wilson and his pupils have shown that in species in 

 which the female contains two X-chromosomes and the male 

 one such chromosome, a new chromosome may appear in the 

 male, a so-called Y-chromosome, which the female does not 

 normally possess. What its precise function is has not yet 

 been ascertained. 



Finally, in many animals no difference has been detected 

 between the chromosome composition of the two sexes, but 

 this does not preclude the existence of such a difference, even 

 though it has not yet been discovered. 



To summarize the foregoing, there are many known facts 

 which support and none which contradict the idea that the 

 female has a greater chromatin content than the male and, 

 either by reason of this fact or independently of it, has 

 greater anabolic activity in reproduction, producing macro- 

 gametes, gametes stored with food. Micro-gametes, those 

 not stored with food but generally possessed of locomotive 

 ability, are the distinctive product of males. 



Morgan (1913) assumes that the chromatin element, which 

 occurs in the female but not in the male, is the specific cause 

 of femaleness, that is, of egg production, and so speaks of the 



