Seal, Walrus, and Manati, are rather generic denominations than
specific names. Under that of the Seal, we shall comprehend, first,
the _phoca_ of the ancients, which is probably the same animal as the
seal; 2. The common seal, which we call the _sea-calf_; 3. The great
seal, of which Mr. Parsons has given a figure and description in the
Philosophical Transactions, No. 496; and 4. The very large seal, which
is called the _sea-lion_, the figure and description of which is given
in Anson's Voyages.
By the _walrus_ we understand those animals commonly called _sea-cows_,
or _sea-horses_. We know of two species of this animal, one found only
in the northern seas, and the other only in the southern, which is
called _dugan_ or _Indian walrus_. And lastly, under that of _manati_,
we comprehend those called _lamantans_, or _sea-oxen_, in St. Domingo,
and other parts of South America, as well as that of Senegal, and other
parts of the coast of Africa, and which seem to be only varieties of
the American species.
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 foetus 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._
[Illustration: FIG. 192._Seal._]
[Illustration: FIG. 193. _Walrus._ FIG. 194. _Manati._]