32 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, Vol. XVI. 



That the generative organs do affect the external appearance of an 

 animal, is fully proved from the results of castration of various animals. 

 Take the case of the distorted horns of castrated deer. 



Again, many birds when kept in confinement refuse to breed and it 

 not infrequently happens that such birds do not attain the full brilliancy 

 of their plumage. " The male and female of the splendid scarlet ibis " 

 writes Darwin, " are alike, whilst the young are brown ; and the scarlet 

 colour, though common to both sexes, is apparently a sexual colour, 

 for it is not well developed with birds under confinement, in the same 

 manner as often happens in the case of brilliantly coloured male birds." 

 I am of opinion that many of the differences in the plumage of the 

 sexes are in some way correlated with the sexual organs. 



As an example of what we may call correlative sexual colouration 

 i may quote the fact that the inside of the mouth of the male hornbill 

 (Buceros bicornis) is black, while that of the female is flesh-coloured. 

 Darwin himself admitted that sexual selection could not account for the 

 inside of the male hornbill's mouth being black, nor can we suppose 

 that this blackness is due to superabundant vitality exhibited by the 

 male. 



Again, the knob on the base of the bill of the Chinese goose (Anser 

 cygnoides) is larger in the male than in the female. As another example 

 of correlative sexual dimorphism, I may mention the difference in the 

 shape of the neck of the mare and the horse. Anyone with a little 

 experience, if made to mount a horse blindfold, can tell when once on 

 its back, from the shape of the neck, to which sex the animal belongs. 



Then, again, there is the case of the condor, cited by Darwin. The 

 iris of this bird is at first dark-brown, but changes at maturity into 

 yellowish-brown in the male, and into bright red in the female. 



As a rule the development of the sexual organs tends to produce, or 

 at any rate to be concomitant with, increased brilliancy of plumage. 

 There are, however, exceptions. Thus Darwin states of certain 

 young woodpeckers, they " have the whole upper part of the head 

 tino-od with red, which afterwards either decreases into a mere circular 

 red line in the adults of both sexes, or quite disappears in the adult 

 females. " This disappearance of a bright colour can only be explained 

 on the Darwinian hypotheses, on the assumption that the tastes of the 

 female are quiet, and that she has persistently selected the male who 



