The birds agree with the mammals in the development of a four-chambered heart, in their warm blood, in their external covering for the skin, and in the development of arrangements and instincts for the parental care of the young. Their line of Evolution has thus been to some extent parallel to that of the mammals. On the other hand, they differ obviously in the structure and function of their fore limbs, in the absence of a diaphragm, and in their special methods for the care of the young, and there can be no doubt that the two groups have had quite different origins in the reptile class.
Fig. 98.—Archiopteryx, a fossil lizard-like bird.
Photo: Underwood.
Fig. 99.—Eagle, with prey.
Fig. 100.—The Kiwi, Apteryx. A practically wingless running bird.
Photo: W. P. Dando.