and on some characteristics of the Reptilian Birds. 319 
What then are the characteristics of Reptiles that may have 
been presented by the inferior or hemitypic Birds? 
prominent distinctions of Reptiles are the following: 
(1.) A covering of scales, or else a naked skin, instead of a 
covering of feathers. 
(2.) A terrestrial creeping mode of life instead of an aerial 
or flying mode. 
(3.) Incomplete circulation, and hence, to some degree, cold- 
blooded, instead of complete, and. warm-blooded. 
ow, as to the young of the Reptilian Birds, it may be in- 
ferred that— 
use of their legs immediately after leaving the egg, and s 
their own food. A brood of Reptilian bird-chicks, with long 
known, the wings only aid in running. 
__ (3.) But the characteristics which have been mentioned under 
(1) and (2) are not of fundamental value, like that of the exist- 
ence of gills in the young of hemitypic Reptiles, or that of the 
semi-oviparous method of reproduction in Odtocoid Mammals; 
and it would seem that there must have been some more pro- 
Reptiles. The heart may have had its four cavities complete, as 
in Birds, and in Grovedile among Reptiles; but, in addition, 
ere may have been a passage permitting a partial mixture 
; es 
its development. This peculiarity in the vascular system of the 
ung Bird of the present day ceases with the beginning of 
i But in the Reptilian birds it may have continued 
