from the topmost branches of one tree to the lower branches 

 of another, after the mode of the " flying-squirrels," and 

 " fijdng-lemur " of to-day. The wing, at this primitive stage 

 of its evolution, was even then, probably, a three-fingered 

 limb, provided with a broad fringe of incipient feathers along 

 its hinder border. At this stage the body would have been 

 less bird-like than that of Archaeopteryx, and have been stiU 

 more like that of the ancestral reptilian stock from which the 

 birds have sprung. That feathers are, so to speak, glorified 

 reptilian scales cannot be certainly demonstrated, but men 

 of Science are generally agreed that this was their origin. 



By the time that Archaeopteryx had come into being, 

 true flight had been arrived at, though probably it could not 

 have been long sustained. As these primitive birds increased 

 in numbers, and spread from the woodlands to the open 

 country, life became more strenuous. New enemies had to 

 be evaded, longer journeys had to be made for food. Only 

 the very best performers on the wing could survive, and thus, 

 in each generation, the failures would be speedily weeded 

 out, while competition among the survivors would raise the 

 standard. We see the result of this " struggle for existence " 

 in the many and varied types of wings, and of flight, which 

 are presented in this book. 



i8 



