SEX DETKRMIXATIOM 



451 



the male gametes have one X chromosome and the other half have 

 no X, but sometimes Y and sometimes simply one chromosome less 

 than the first type of male gametes. We can then speak of the two 



Fig. 94. — An armadillo egg about six weeks after fertilization, showing the 

 quadruplet foetuses are derived from the single egg and all destined to be of the 

 same sex. (Frotn Newtnan.) 



sexes produced by union of male and female gametes simply in terms 

 of the X chromosomes, females being characterized by XX (duplex) 

 and males by X (simplex). 



SEX DETERMINATION IN PARTHEXOGENETIC SPECIES 



Although it was at first thought that the facts of parthenogenesis 

 (development of eggs without fertilization) was opposed to the 

 chromosomal mechanism of sex determination, further study of this 



