INTERSEXES 



253 



This evidence from triploids gives no specific informa- 

 tion as to the occurrence of genes for sex-determination. 

 If we think of the chromosomes only in terms of genes, it 

 follows that genes are involved, but the evidence does not 

 show what they are like. Even if genes are involved, we 



Fig. 139. 



To the left the female type of intersex of Drosophila, as seen from 

 above and below. The chromosome groups show two X's, three each 

 of the larger autosomes (II and III) and usually (two here) small 

 IV-chromosomes. To the right the male type of intersex, as seen from 

 above and below. The chromosome group has two X 's, three each of 

 II and III, and usually only two IV 's (here three). 



cannot state whether there is one gene in the X that 

 stands for femaleness, or hundreds of such genes. Simi- 

 larly for the ordinary chromosomes — the evidence does 

 not tell us whether the genes for maleness, if there be 

 such, are in all the chromosomes or in only one pair. 



There are, however, two ways in which we may hope, 

 some day, to discover something about the genes that 

 influence sex. The X-chromosome may become frag- 

 mented in such a way as to reveal the location of the spe- 

 cial genes relating to sex, if there are such. The other 

 hope rests on the occurrence of a gene mutation. If other 



