92 INSECT PHYSIOLOGY 



genetic make-up of the body cells - the secondary characters are not 

 evoked by internal secretions from special glands, either in the 

 gonads themselves or elsewhere. For (i) removal or transplantation 

 of the gonads at any stage of life is without effect upon the secondary 

 sexual characters; (ii) where the genetic constitution, in respect to 

 sex, of some body cells differs from that of others, a sexual mosaic or 

 gynandromorph results, parts of which are entirely male and other 

 parts entirely female; and (iii) if the wing germs of Lepidoptera of 

 one sex are transplanted into the other sex, their sexual characters 

 are not influenced by their new environment. 



But in insects, as in other animals, the genetic sex can be over- 

 ridden by other factors, and it is these other, physiological, factors in 

 which we are interested here. The phenomena are most conveniently 

 described in terms of Goldschmidt's well-known theory of inter- 

 sexes. Leaving aside the genetical analysis, this theory supposes that 

 sex is determined by a quantitative balance between male determin- 

 ing and female determining factors within the nucleus of every cell. 

 By analogy with the hormones of the animal body, these competing 

 influences are often pictured as being chemical in nature (although, 

 of course, they might be of some quite other kind) - that is, as 

 hormones working inside the cell. 



In the normal female the quantitative influence of the female 

 determining factor outweighs that of the male; but the male factor 

 is still there, and under certain circumstances its effect may become 

 manifest. Thus, the balance between these factors, though normally 

 determined according to the laws of genetics, may (according to those 

 who accept this interpretation of the facts) be upset in several ways, 

 (i) By crossing races in which the sex determining factors are of un- 

 matched strength. Hence 'intersexes' result, the morphological 

 characters of which are best explained by supposing that, owing to a 

 difference in the rate at which the male and female factors come to 

 exert their influence, the insect has developed up to a certain point 

 as one sex and then 'switched over' to complete its development as 

 the other, (ii) By abnormal external temperatures, which are sup- 

 posed again to upset the rate at which the two factors work, in such 

 a way that the latent factor, which would normally be suppressed, 

 is able to exert its specific effect, so that intersexual forms result. 



