460 The Descent of Man. Past 11. 



?.oloured, but I hear from Mr. Sclater, that this appears to be the 

 case with the Musophaga) or plantain-eaters. Nor do I believe 

 that any large group exists in which the sexes of all the species 

 are widely dissimilar in colour : Mr. Wallace informs me that 

 the chatterers of S. America (Voting idee) offer one of the best 

 instances ; but with some of the species, in which the male has a 

 splendid red breast, the female exhibits some red on her breast ; 

 and the females of other species shew traces of the green and 

 other colours of the males. Nevertheless we have a near 

 approach to close sexual similarity or dissimilarity throughout 

 several groups : and this, from what has just been said of the 

 fluctuating nature of inheritance, is a somewhat surprising- 

 circumstance. But that the same laws should largely prevail 

 w r ith allied animals is not surprising. The domestic fowl has 

 produced a great number of breeds and sub-breeds, and in these 

 the sexes generally differ in plumage ; so that it has been 

 noticed as an unusual circumstance when in certain sub-breeds 

 they resemble each other. On the other hand, the domestic 

 pigeon has likewise produced a vast number of distinct breeds 

 and sub-breeds, and in these, with rare exceptions, the two sexes 

 are identically alike. Therefore if other species of Gallus and 

 Columba were domesticated and varied, it would not be rash to 

 predict that similar rules of sexual similarity and dissimilarity, 

 depending on the form of transmission, would hold good in both 

 cases. In like manner the same form of transmission has gene- 

 rally prevailed under nature throughout the same groups, 

 although marked exceptions to this rule occur. Thus within 

 the same family or even genus, the sexes may be identically alike, 

 or very different in colour. Instances have already been given 

 in the same genus, as w 7 ith sparrows, fly-catchers, thrushes and 

 grouse. In the family of pheasants the sexes of almost all the 

 species are wonderfully dissimilar, but are quite alike in the 

 eared pheasant or Crossoptilon auritum. In two species of 

 Chloephaga, a genus of geese, the male cannot be distinguished 

 from the females, except by size ; whilst in two others, the sexes 

 are so unlike that they might easily be mistaken for distinct 

 species. 29 



The laws of inheritance can alone account for the following 

 cases, in which the female acquires, late in life, certain characters 

 proper to the male, and ultimately comes to resemble him more 

 or less completely. Here protection can hardly have come into 

 play. Mr. Blyth informs me that the females of Oriolus melano- 

 ctphalus and of some allied species, when sufficiently mature to 

 breed, differ considerably in plumage from the adult male? ; but 

 ** The < Ibis,' vol. vi. 1864, p. 122. 



