3550. The development of the young makes an essential distinction upon a large scale, since one great body of Birds must be fed as nestlings, whilst the other, when scarcely emerged from the egg, runs about and seeks its own nourishment. Although in the lower animals the young do not require the assistance of the parents, and, on the other hand, those of the Thricozoa are suckled for a longer time by the mother; yet still those Birds which can, upon issuing from the egg, at once nourish themselves, such as the Fowls, Geese, &c., are probably the most perfect, for they pass parallel to the upper classes of animals, and for the Ostrich to be a Thricozoon, there is indeed as little wanting as to the Crocodile.
3551. There is no doubt whatever that the Natatores in every respect, both in the structure of the feet and head as also in their mode of living and feeding, repeat the Fishes. This opinion the empirical zoologists have already adopted from the Physio-philosophy.
The same may be said of the Grallæ or Wading Birds in reference to the Reptiles. Their feet, neck, and beak are serpentiform, and associated with a frog-like body. Their mode of living and feeding is likewise amphibious. But these birds pass over so directly into the Fowls, that the latter could not be arranged elsewhere, apart even from their displaying by their domestication to Man the higher grade of understanding, which is manifested for the first time in the class of Birds.
The Bustards and Ostriches are, finally, the highest stage of Birds, and form the closest alliance with the Thricozoa.
3552. This point being once settled, it is self-evident that the Birds, which do not stand in need of being fed, occupy the uppermost place, and consequently the nestling or parent-fed Birds the lowest, i. e. the former correspond to the Sarcozoa, the latter to the Dermatozoa.
A. SPLANCHNIC BIRDS.—NESTHÖCKER.
3553. Remain, after exclusion from the egg, in the nest and are fed; neck and feet short, toes four in number and ununited, beak pointed.
By their short neck, which rarely appears longer than the head, these Birds approximate the Reptiles and Fishes, in whom also the head has scarcely separated itself from the thorax.
The uniformity of the feet and toes is likewise an inferior character, as it is found in the Dermal Reptiles and Fishes; while in the Sarcose Reptilia and Fishes the feet and fins make their appearance in the greatest variety, both as regards the form and length of the feet themselves, as the structure of the toes; and such is the case too in the higher organized Birds.
The same holds good also of the form of the head, and especially of the maxillæ and teeth, which are very uniform in the lower Fishes and Reptiles, but occur under very varied conditions in the upper kinds, exactly as in the Natatores and Grallæ, in the Gallinæ and Struthionidæ,