INTRODUCTION xxix 



such a direct effect of one kind or another is in many- 

 instances produced. But in all such matters one would 

 like to see experimental proof and to have full chemical 

 explanation of the details of the coloration and the way 

 in which external conditions directly modify it. Mr. 

 Pycraft thinks that a humid atmosphere undoubtedly 

 causes an intensification of pigment inclining to melan- 

 ism. That would be very important if it were experi- 

 mentally demonstrated, but that seems not to be the 

 case, nor is the chemical change by which such intensi- 

 fication of pigment, or the production of independent 

 black pigment, could be arrived at by the action of a 

 humid atmosphere as yet suggested. Our author says 

 that of course natural selection " may have " acted by 

 securing elimination of all those individuals which were 

 not physiologically affected by desert conditions, viz., 

 intense light and heat, or (I should be inclined to add) 

 were not, owing to other causes, variations in the direction 

 of sand-colour. 



In regard to the life-history of birds, Mr. Pycraft 

 has drawn attention to a host of facts which have 

 hitherto been ignored by leading Darwinians, though 

 of first-rate importance from their point of view. Such 

 are his own observations as to the coloration of nestlings 

 and of immature birds showing the significance of striped 

 nestlings and of the brilliantly coloured mouths of certain 

 species. He gives very cogent reasons for regarding 

 the ancestral bird as arboreal, and as gradually acquiring 

 flight by "parachuting". The view that the earliest 

 birds were aquatic and that the wing was at one time a 

 paddle is, however, still capable of defence. To arrive 

 at anything like a preference between the two theories 

 requires a very extensive survey of anatomical and 

 palseontological facts, as well as a consideration of the 



