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 
Archxopteryx 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 
