go 



THE BRITISH NATURALIST. 



[MA.Y 



because it is not certain that even Archc^opferyx possessed feathers so 

 highly specialized as those of existing birds, and as we have evidence 

 that the early reptilian ancestors of birds were covered with simple 

 feathers, we have the fact that chicks go through their first moult in the 

 shell. These first feathers are long fine hair-like and barbless, and 

 represent the early simple feathers which some of the tree-lizards were 

 clothed with. What other explanation can be offered for the presence 

 and loss of feathers which pass away before the chick lea'ves the shell. 

 This embryonic moult is succeeded by the ordinary highly specialized 

 feathers possessed by most existing birds. 



It may be also mentioned that some birds possess spurs on their 

 wings which are representatives of the claws of their reptilian 

 ancestors ; and in some species the young use their wings like legs for 

 crawling. The most remarkable instance of this is the Hoatzin, whose 

 young not only have claws on the pollex and index, but in some 

 individuals those organs are opposable ; in other words the young 

 Hoatzin not only has what corresponds to our thumb and first finger* 

 and to the homologous toes on the lizard's fore-feet, I)ut it has claws 

 at their extremities and it travels on all fours. In the adult the claws 

 become mere warts, and the bird, though loth to rise, can fly well ; 

 but the fact that a young bird before it has got the power of flight 

 uses its fore-limbs as legs is surely some evidence for the theory of 

 descent from a feathered lizard ; this habit is not confined to the 

 Hoatzin, but has been observed in at least one group of British birds, 

 the Grebes. 



In speaking of the fore-limbs of birds, we are reminded of a feature 

 in tlieir skeletal structure which is characteristic of all existing birds. 

 The metacarpal bones, homiOlogous to those of the palm of the hand 

 in man, are fused, but in the famous fossil birds Archcsopteryx 

 r.iacvitva, though in no other known species, these bones remain 

 distinct as in reptiles. Moreover the three digits were in Archceopteryx 

 armed with claws and these facts are of great interest since they point 

 out clearly the close relationship oi Archceopteryx to the reptilian form 

 from v.'liich it had sprung. The interest of this fact is not lessoned 

 by the knowledge revealed to us by embryology that all modern birds 

 pass through a stage in their development similar to that which was 

 permanent in ArchcBopteryx, i.e., all embryo birds have the metacarpals 

 free, but before the hatching takes place, the metacarpals become 



