COLORATION in 



Hitherto we have always regarded the development of 

 conspicuously coloured areas such as these as the product 

 of " sexual selection," and even when they may be present 

 in the female this interpretation is still regarded as valid ; 

 for it is assumed that, though originally developed as a 

 male sexual adornment, they have been, in such cases, 

 transmitted to the female, as we have already seen is often 

 the case with brilliant plumage. 



The nestlings of Passerine birds, almost without 

 exception, have the mouth parts more or less brilliantly 

 coloured. Usually this takes the form of a more or less 

 extensive fleshy flange, or rim surrounding the gape, of 

 a bright yellow colour. But in some species there occur, 

 in addition, at_the angle of the gape, globular or bead-like 

 outgrowths of bare skin, and brilliantly coloured. In the 

 Gouldian weaver-finch these bodies are of a brilliant 

 opalescent emerald green and blue, and the roof of the 

 mouth is marked by five black symmetrically disposed 

 spots, while a black bar crosses the tongue. The nestling 

 of the crimson-eared waxbill, and of the parrot finches, 

 are similarly marked, while the red-tailed weaver-finch of 

 Samoa has bright red wattles. 



Mention has just been made of black spots within the 

 mouth cavity. These occur in quite a number of the 

 nestlings of our native birds, and are made the more 

 conspicuous by reason of the brilliant background in which 

 they are set. As a rule this background is yellow, and 

 the spots may be few in number, or absent altogether. 

 In the young hedge-sparrow the background is yeUow, 

 and the tongue-spurs are each marked by a black spot. 

 In the skylark there are three black spots, arranged in 

 the form of a triangle on the tongue, and a fourth near 

 the top of the lower jaw. But the high-water mark of 



