THE SOCIAL INSECTS 



genetic origin of castes comes from the study of various 

 abnormal individuals. Very occasionally specimens are found 

 which may Be called sex-mosaics. These have part of the 

 body female, part male, with the areas often sharply marked 

 off from one another. Where the male and female are different 

 in size, shape and colour, such mosaics are asymmetrical and 

 look very peculiar. Analogous mosaics which are male- 

 worker, male-soldier, queen-worker, soldier-worker and 

 soldier-queen, have also been found. 



The origin of one kind of male-female mosaic, known as 

 a gynandromorph, is fairly well understood. During develop- 

 ment, some particular cell divides abnormally, so that one 

 daughter cell receives a full set of the hereditary material 

 (chromosomes), whereas the other gets only a half set: 

 the latter, in the Hymenoptera, results in a male. All those 

 parts of the body which later develop from the subdivision 

 of the abnormal cell become male, and form an island or 

 islands of maleness in a predominantly female individual. 

 It was suggested by Wheeler that the other mosaics, such as 

 the queen-worker, might arise in an analogous way. This 

 would imply that the caste of each individual is genetically 

 determined in the egg. 



There is, however, another type of sex mosaic, the inter- 

 sex, which may be described as a mosaic in time rather than 

 in space. In the gypsy moth, for instance, every cell of the 

 body produces substances which influence development in 

 the direction of either maleness or femaleness. If the physio- 

 logy of development is disturbed, there may at first be an 

 excess of the female-promoting substance but later of the 

 male-promoting one. The parts of the body which in develop- 

 ment reach their final form first will then be female, while 

 those which develop later will be male. The mosaics so pro- 

 duced tend to be of a type in which male characters chiefly 



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