496 The Determination of Sex 



appear in some of the higher forms as an abnormal condition, 

 but it is doubtful whether true hermaphrodites are ever found 

 among mammals. Certain intersexes such as the diploid inter- 

 sexes of Drosophila pseudoobscura might be regarded as her- 

 maphrodites because they possess two sets of reproductive organs, 

 one male-like and the other female-like. Dobzhansky and Spas- 

 sky, however, prefer to regard them merely as intersexes because 

 the reproductive organs that are present consist of genital ducts 

 and external genitalia, but not gonads. It is probably preferable 

 to restrict the term hermaphrodite to those animals in which 

 actual, functional gonads of both sexes are present. These inter- 

 sexes, however, approach the true hermaphroditic condition much 

 more closely than the triploid intersexes of Drosophila or the 

 diploid intersexes of Lymantria. 



Gynandromorphs 



In a few species individuals have been found, although rarely, 

 which are composed of both genetically male and genetically 

 female tissues. The two types of tissue may differ in extent, 

 and theoretically such an individual may vary from a condition 

 in which exactly half the body is of one sex and the other half 

 is of the other sex to a state in which only one cell is male and 

 the remainder of the body is composed of female tissue. Many 

 sexual mosaics are bilaterally symmetrical; that is, one half the 

 body is male and the other half female, and the boundary is the 

 midventral line that runs lengthwise through the center of the 

 body. This condition appears to arise during very early embry- 

 ology in those animals in which the first cleavage division divides 

 the fertilized egg into two cells, each of which will ultimately 

 develop into one side of the body. If at about this first cleavage 

 in an XX female one of the X chromosomes is lost or otherwise 

 inactivated in one of the two cells, the side of the body which 

 develops from it will be male whereas the side that develops 

 from the cell which has retained two functional X chromosomes 

 will be female. 



A mitotic or other abnormality occurring at the first cleavage 

 division cannot so readily explain gynanders in insects, for insects 

 do not undergo cleavage divisions in the same manner as most 

 animals, and the first cleavage does not divide the right from the 

 left side. In insects, the egg is centrolecithal. The nucleus lies 



