310 THE WORLD OE LIFE 



parentlj free and movable digits on the fore limbs, each end- 

 ing in a distinct claw ; while the two bones forming the fore- 

 arm appear to have been also free and movable, so that the 

 wing must have been much less compact and less effective for 

 flight than in modern birds. This bird was about as large as 

 a rook, but with a tail of twenty vertebra', each about half an 

 inch long and bearing a pair of feathers, each four inches in 

 length and half an inch broad, while the wing feathers were 

 nearly twice as long. The almost complete disappearance of 

 the unwieldy tail, with the fusing together of the wing-bones, 

 must have gone on continuously from that epoch. In the 

 Cretaceous period the long tail has disappeared, and the wing- 

 bones are much more like those of living birds; but the jaws 

 are still toothed. In the early Tertiary deposits bird-remains 

 are more numerous, and some of the chief orders of modern 

 birds seem to have existed, while a little later modern families 

 and genera appear. 



The important point for our consideration here is that, in 

 the very earliest of the birds yet discovered which still re- 

 tained several reptilian characteristics, true feathers, both of 

 wings and tail, are so clearly shown as to leave no doubt of 

 their practical identity with those of living birds. 



It is therefore evident that birds with feathers began to be 

 developed as early as (perhaps even earlier than) the mem- 

 branous-winged reptiles (Pterodactyles), and that these two 

 groups of flying vertebrates began on two opposite principles. 

 The birds must have started on the principle of condensation 

 and specialisation of the fore limb exclusively for flight by 

 means of feathers ; the other by the extension of one reptilian 

 digit to support a wing-membrane, while reserving the others 

 probably for suspension, as in the case of the thumb of the 

 bats. 



The Marvel and Mystery of Feathers 



Looking at it as a whole, the bird's wing seems to me 

 to be, of all the mere mechanical organs of any living thing, 



