SEX-CHARACTERS ILLUSTRATED 57 



arising in the same way in the embryo, may 

 come to be so different that even on external 

 inspection the two sexes can be distinguished 

 at a glance. Thus in most Mammals the 

 testes are carried in an external pouch or 

 scrotum (into which they descend, as if by 

 a sort of normal rupture, at a certain stage 

 in development), while the ovaries always 

 remain internal. 



In the second place, the dimorphism may 

 be expressed in conspicuous differences in 

 the accessory reproductive organs, such as 

 egg-laying structures or ovipositors in the 

 females and organs for effecting sexual union 

 in the case of the males. Thus every one 

 knows that drone-bees have no sting, for a 

 sting is a transformed ovipositor turned to 

 a new use, and is therefore confined to 

 the queen-bees (functional females) and the 

 worker- bees (usually sterile females). A male 

 spider is clearly marked off from his mate by 

 the extraordinary transformation of the tips 

 of the second pair of mouth-parts the pedi- 

 palps into organs which are used in transfer- 

 ring the fertilising spermatozoa into the female. 



In the third place, the dimorphism may be 

 expressed in peculiarities, like antlers, manes, 

 combs and spurs, which have nothing directly 

 to do with reproduction, but which the males 

 have and the females have not. In a number 

 of less familiar cases, the female has structures 

 which are conspicuous by their absence in 

 the males, though in these cases it must be 

 confessed that the males are more or less 

 degenerate. Thus many a male Rotifer has 

 no food-canal, and the male of a remarkable 



