topmost branches of one tree to the lower branches of another, 
after the mode of the “ flying-squirrels,” and “ flying-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 
Archzopteryx, and have been still 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 Archeopteryx 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. 
18 
