TABOO AND GENETICS 23 



maturation are not exactly alike as to chromo- 

 some composition. All the eggs contain what 

 is known as the " X " type of sex chromosome. 

 But only half the male sperm have this type 

 — in the other half is found one of somewhat 

 different type, known as " Y." (This, again, 

 is for the human species — in some animals the 

 mechanism and arrangement is somewhat dif- 

 ferent.) If a sperm and egg both carrying the 

 X-type of chromosome unite in fertilization, the 

 resulting embryo is a female. If an X unites 

 with a Y, the result is a male. Since each 

 combination happens in about half the cases, 

 the race is about half male and half female. 



Thus sex is inherited, like other characters, 

 by the action of the chromatin material of the 

 cell nucleus. As Goldschmidt (i) remarks, this 

 theory of the visible mechanism of sex distribu- 

 tion " is to-day so far proven that the demonstra- 

 tion stands on the level of an experimental 

 proof in physics or chemistry." But why and 

 how does this nuclear material determine sex ? 

 In other words, what is the nature of the process 

 of differentiation into male and female which 

 it sets in motion ? 



To begin with, we must give some account of 

 the difference between the cells of male and 

 female origin, an unlikeness capable of producing 

 the two distinct types of gametes, not only in 

 external appearance, but in chromosome makeup 



