BIRDS OF OLD 73 



stretched fingers, the thumb alone being left 

 free, while in the pterodactyl the thumb is 

 wanting and the membrane supported only by 

 what in us is the little finger, a term that is a 

 decided misnomer in the case of the pterodac- 

 tyl. In birds the fingers have lost their in- 

 dividuality, and are modified for the attach- 

 ment or support of the wing feathers, but in 

 Archffiopteryx 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 develop- 

 ment 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 



