THE GENEALOGY OF ANIMALS 87 



the ' slow, cold-blooded, scaly saurian ever became 

 transformed into the quick, hot-blooded, feathered 

 bird, the joy of creation,' is a considerable mys- 

 tery, yet we know no reason for believing that the 

 transformation did not take place. Although in 

 their external appearance and mode of life birds 

 and reptiles differ so widely from each other, yet, 

 in their internal structure and embryology, they 

 are so much alike that one of the brightest 

 anatomists that has ever lived (Huxley) united 

 them both into a single class under the name 

 Sauropsida. It might naturally be supposed that 

 the birds are descendants of the flying reptiles, 

 the pterosaurs. But this may not be true. The 

 pterosaurs were structurally much further removed 

 from the birds than were certain extinct terrestrial 

 reptiles. The fact that birds and pterosaurs both 

 had wings has really nothing to do with the case. 

 For the wings of reptiles, we almost know, were 

 not homologous with the wings of birds. The 

 bird's wing is a feathered fore-leg ; the wing of the 

 reptile was an expanded skin stretching from the 

 much-elongated last finger backwards to the hind- 

 leg and tail. Wings, it may be remarked in 

 passing, have had at least four different and 

 distinct beginnings in the animal kingdom, repre- 

 sented by the bats, the birds, the reptiles, and the 

 insects. This does not include the parachutes 

 of the so-called flying squirrels, lemurs, lizards, 

 phalangers, and fishes. 



The first birds had teeth and vertebrated tails. 

 The archeopteryx, which is the earliest toothed 



