238 



A HISTORY OF BIRDS 



ately — as more nearly approaching Archaeopteryx (p. 250), and 

 the proto-avian types, than any other living member of the 

 Class Aves. 



But it is in the nestling that these primitive features stand 

 revealed. Had the adult alone been known they would never 

 have been .suspected. The nestling, however, presents the key 

 to the whole question concerning the evolution of the two types 

 of nidifugous and nidicolous young, and furthermore, explains 

 the true meaning of the vestigial claws which occur on the 

 wings of adults of the most diverse types. 



III. 27. — HoATZiN (Opisthocomus cristatus) 



Briefly, the history of the nestling of this strange bird is as 

 follows. Nidifugous, or, to use the simpler term, precocious 

 it is hatched in a rough nest of sticks placed amid the boughs 

 of a tree overhanging the water. How long after the escape 

 from the egg it and its nest-fellows remain in the nest is not 

 known, but they probably use this, after the first few hours of 

 independent life, only as a roosting-place where they can be 

 " brooded " by the mother. The hours of daylight appear to be 

 passed in rambling about the tree in which the nest is placed. 

 The method of progression is so far unique, since not only are 

 the feet and the beak used Parrot-fashion, but the wings are 



