102 THE INFANCY OF ANIMALS 



phases — a longitudinally striped phase, a spotted or 

 mottled phase, due to the disintegration of the stripes, 

 and a uniformly coloured phase representing a plumage 

 from which these spots and mottlings have faded. This 

 process of transformation is also met with among the 

 mammals. But among birds, it will be noted, transverse 

 stripes are conspicuous by their absence : this is true at 

 any rate for nestlings, though some adults display a more 

 or less distinctly transversely barred dress. 



What relation, it may now be asked, do these phases 

 of coloration bear to the present-day needs of their 

 wearers ? Are they merely survivals from a remote past, 

 displaying a more or less marked tendency to disappear ; 

 or do they fulfil any useful purpose ? Do they answer 

 to ancestral adult or to ancestral nestling liveries ? All 

 the evidence, surely, goes to show, as we have already 

 indicated, that in discussing this matter we must consider 

 the striped plumage as answering to an ancestral livery, 

 whether of an adult or nestling stage, and the mottled 

 and whole-coloured nestUng plumages as derived therefrom 

 by the gradual disintegration of the stripes. Where the 

 stripes have preserved their integrity in existing nestlings 

 we must hold that they still serve the purpose for which 

 they were originally evolved. That is to say, the con- 

 ditions of existence which determined the evolution of a 

 striped livery ages ago are essentially the same to-day. 



Similarly, the coloration of young birds, such as terns, 

 gulls, and plovers, may almost certainly be regarded as 

 having been evolved — by the disintegration of stripes — 

 to harmonise with their surroundings. They are " pro- 

 tected resemblance " or " procryptic " colours, investing 

 the wearer with a veritable mantle of invisibility. How 

 perfectly these mottlings blend with their surroundings 



