It has been proposed to separate the Brevipennes, or short-winged birds, from the Grallatores, and erect them into a separate order.
The Reptiles, of which the majority possess the faculty of living upon land and in water,—whence their name of Amphibia,—never pass beyond the limits of warm and temperate climates: their blood, which has the same temperature as the medium wherein they live—whence their name of "cold-blooded animals"—does not circulate where the mean annual temperature descends below freezing-point. Yet frogs and salamanders have been met with in Greenland, and on the banks of the Mackenzie River, in North America, under 67° latitude.
Linnæus was not acquainted with more than 215 species of Amphibia, divided into four orders:—the Chelonians, or tortoises; the Saurians (as the lizard and crocodile); the Ophidians (serpents); and the Batrachians (frogs). In 1789, Lacépède raised the total to 303; in 1820, Merrem estimated it at 677. At present, the number of species of Reptilia classified and described amounts to 2000, and the four orders into which they are distributed are—
1. Ophidia, or Serpents.
2. Sauria, or Lizards.
3. Loricata, or Crocodiles.
4. Chelonia, or Tortoises.
According to Sching, there are 7 tortoises, 33 serpents, and 35 lizards.
Fishes are the least known of those superior animals whose skeleton and vertebral column are situated in the interior of the body, and which are thence named Vertebrata. The richest collections, such as those of the British Museum, and those of the Museum of Natural History in Paris, which contain about 3000 species, do not represent probably more than a fourth of the existing total, including fresh-water and salt-water fish. How many rivers and streams in both hemispheres still remain to be explored! How far we are from a knowledge of the fishes which people the different strata of the great ocean.
Agassiz divides this great class of vertebrated animals into the four orders of Cycloid, Ctenoid, Placoid, and Ganoid, according to the character of their scales. Cuvier, into Osseous fishes (with true bones), and Cartilaginous; subdividing the former into Acanthopterygii and Malacopterygii.
The difficulty of the problem we are here considering increases when we come to the inferior animals. Who would pretend to determine the number of species of Mollusca which inhabit the earth, the fresh waters and the salt? This much is certain, that it cannot be less than that of the Vertebrates.
In the vast aggregate of the Articulata, the inquirer finds himself utterly astray and bewildered. This great division is not divided into those which have, and those which have not, articulated members.