Chap, XV. COLOUR AND NIDIFICATION. 177 



with the slisfht differences between the sexes of those 

 birds which build concealed nests. On the otlier hand, 

 the differences in colour between the sexes, whether 

 great or small, may to a large extent be explained 

 on the principle of the successive variations, acquired 

 by the males through sexual selection, having been 

 from the first more or less limited in their transmission 

 to the females. That the degree of limitation should 

 differ in different species of the same group will not 

 surprise any one who has studied the laws of inheritance, 

 for they are so complex that they appear to us in our 

 ignorance to be capricious in their action.^^ 



As far as I can discover there are very few groups 

 of birds containing a considerable number of species, 

 in which all have both sexes brilliantly coloured 

 and alike ; but this appears to be the case, as I hear 

 from Mr. Sclater, with the Musophagse or plain- 

 tain-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 (Cotingidse) 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 some- 

 what surprising circumstance. But that the same 

 laws should largely prevail with allied animals is 

 not surprisiug. The domestic fowl has produced a 



^ See remarks to this effect in my work on ' Variation under Domes- 

 tication,' vol. ii. chap. xii. 



VOL. II. N 



