SEXUAL SELECTION 351 



come transmitted to the females, and finally to the young 



(p- 273)- 



In this last connection it is significant to notice that the 

 young of many species of Warblers are more brilliant than their 

 parents. From which it may be inferred that this evanescent 

 beauty is reminiscent of an earlier adult dress, more richly 

 coloured than that worn to-day. 



It is a noteworthy fact that in nearly every large genus, or 

 any collection of genera in any given family of birds, more or 

 fewer lines of evolution in the development of resplendent 

 coloration, starting from dull-coloured species, will be found. 

 The Pigeons, Swallows, Kingfishers and Touracos may serve 

 as illustrations of this fact, but they may be found by the 

 score. The same law, in short, holds in regard to genera which 

 obtains in regard to species. That is to say, in any given family, 

 e.g., Kingfishers, one can start with a genus of dull-coloured 

 species, some of which show evidence of incipient brilliancy, 

 and from thence one can trace several lines of distinctive 

 coloration — grey and white, black and white, blue and \%hite, 

 blue and red, and red ; the several species in the respective 

 genera, belonging to any given line of coloration — black, blue 

 and white, or blue and red — showing various combinations of 

 these colours whereby they are specifically distinguished. Here, 

 too, in the dull-coloured species the sexes differ, and the young 

 resemble the female; in the brightly coloured species, male, 

 female and young are alike. 



The measure of a bird's consciousness of the effect he pro- 

 duces, is one difficult to estimate. Can there, as a matter of 

 fact, be any but the most vague conception in the mind — if we 

 may use this term — of the actor of the appearance he presents 

 to his mate ? In many cases this display must be before an 

 audience of one. There can be no model to serve as a mirror, 

 and it is an assumption to suppose that even in the presence 

 of such a mirror there is sufficient intelligence to make the 

 actor realise that the model, albeit his rival, is, as it were, a 

 reflection of himself. Yet, as may be gathered from the fore- 

 going instances, these birds behave as if they were conscious 

 of their appearance. To the list of illustrations let us add yet 

 another. The Kagu (Rhinochcetus jubatus) of New Caledonia, 

 when excited, sexually or otherwise be it noted, raises the 



