BIRDS OF OLD 53 



wings, it may be said that they are made on very 

 different patterns in such animals as the pterodactyl, 

 bat, and bird, and that while the end to be achieved is 

 the same, it is reached by very different methods. The 

 wiag membrane of a bat is spread between his out- 

 stretched fingers, the thumb alone being left free, while 

 in the pterodactyl the thumb is wanting and the mem- 

 brane supported only by what in us is the little finger, 

 a term that is a decided misnomer in the case of the 

 pterodactyl. In birds the fingers have lost their in- 

 dividuality, and are modified for the attachment or 

 support of the wing feathers, but in Archseopteryx the 

 hand had not reached this stage, for the fingers were 

 partly free and tipped with claws. 



We get some side lights on the structure of primitive 

 birds by studying the young and the earlier stages of 

 living species, for in a very general way it may be said 

 that the development of the individual is a sort of rough 

 sketch or hasty outline of the development of the class 

 of which it is a member; thus the transitory stages 

 through which the chick passes before hatching give us 

 some idea of the structure of the adult birds or bird-like 

 creatures of long ago. Now, in embryonic birds the 

 wing ends in a sort of paw and the fingers are separate, 

 quite different from what they become a little later on, 

 and not unlike their condition in Archseopteryx, and 

 even more like what is found in the wing of an ostrich. 



Then, too, there are a few birds still left, such as the 

 ostrich, that have not kept pace with the others, and 

 are a trifle more like reptiles than the vast majority 

 of their relatives, and these help a little in explaining 

 the structure of early birds. Among these is a queer 

 bird with a queer name, Hoactzin, found in South 

 America, which when young uses its little wings much 

 like legs, just as we may suppose was done by birds of . 



