The seal and the walrus approach nearer to quadrupeds than to cetaceous animals, because they have a kind of feet. But the manatis, which have only two before, are more of the cetaceous tribes than the quadrupeds. But they differ from every other animal by the following striking character. They are the only animals that can equally live in air and water, and consequently the only ones we can properly term amphibious. In man, and the other terrestrial viviparous animals, the foramen ovale of the heart, which permits the fœtus to live without respiration, is shut at the moment of its birth, and remains closed during life. In these, on the contrary, it is always open, notwithstanding the females bring forth their young on land; and their respiration begins and operates immediately after birth, as it does in every other animal. By means of this perpetual aperture in the septum, subsisting and permiting the communication of the blood from the vena cava to the aorta, these animals have the advantage of breathing or not at pleasure. This singular property is common to all three; but each has peculiar faculties, which we shall notice as far as possible, in the history of the different species.
Engraved for Barr’s Buffon.
FIG. 192.Seal.
FIG. 193. Walrus. FIG. 194. Manati.
