CHAPTER XVI 



INTERSEXES 



IN recent years some curious individuals have been 

 found in species with separate sexes, that combine 

 to varying- degrees the characters of males and fe- 

 males. At present most of these intersexes, or sex inter- 

 grades, may be referred to four sources: (a) to changes 

 in the ratio of the sex-chromosomes to the rest of the 

 chromosomes ; (b) to changes in the genes not visibly 

 connected with changes in chromosome number; (c) to 

 changes that result from crossing wild races, and (d) to 

 changes in the environment. 



Intersexes from Triploid Drosophila. 



To the first class of intersexes belong some of the off- 

 spring of triploid females of Drosophila. When the eggs 

 of a triploid female mature, the chromosomes are irregu- 

 larly distributed, and, after the polar bodies have been 

 given off, the eggs are left with different numbers of 

 chromosomes. If such a female is mated to a normal male 

 whose sperm carries one set of chromosomes, the off- 

 spring that come through are of several kinds (Fig. 138). 

 There is reason to believe that many eggs do not develop 

 at all, because they lack the right combination to produce 

 a new individual; but amongst the survivors there are 

 some triploids, more diploids (normals), and a few inter- 

 sexes. These intersexes (Fig. 139) have three sets of 

 autosomes and two X-chromosomes (Fig. 138). The for- 

 mula is 3a+2X (or 3a+2X+Y). Thus, although the 

 intersex has the same number of X-chromosomes as has 



