98 
MAMMALIA. 
the thickness and fineness of which increases with the severity 
of the climate they inhabit, and which is covered by rather coarse 
hairs lubricated with oil, the object of which is to prevent the 
water from penetrating to the skin. A thick layer of fat protects 
the body against the cold, more especially in those species which 
inhabit the extreme frigid regions. 
The Amphibia have the head rounded, the eyes large, the 
auditory conch rudimentary or null, the upper lip covered with a 
thick moustache. Their jaws have three sorts of teeth, and the 
brain is furrowed into numerous circumvolutions. Living in 
numerous troops, they feed on Fishes, Mollusks, Crustaceans, &c. 
They dive with great facility ; and although obliged to come to 
the surface to breathe they can remain a long while under water. 
This circumstance is explained by a peculiarity in their circulating 
apparatus. They are provided with vast venous reservoirs, in 
which the blood accumulates whilst the lungs are inactive. The 
animal is not suffocated on that account, however ; for asphyxia, or 
suffocation, is brought on by the stoppage of the circulation of the 
blood, as soon as respiration is suspended; but the sinus provides 
this circulation in the pulmonary cells whilst the animal is under- 
neath the surface. 
Owing to this precaution of nature, the Amphibia can wander 
freely about in the depths of the ocean in search of their 
food ; it is only when the blood overruns their venous reser- 
voirs that they find it necessary to remount to the surface to 
breathe. 
As their members are badly fitted for locomotion on land [in 
most instances], the Amphibia only leave the water when they 
want to sleep, to give birth to or suckle their young. Under 
such circumstances, when they are surprised on the shore, they 
are quite at the mercy of their assailants ; for they are equally 
incapable of escaping from, and of resisting those who attack 
them. One must not be surprised, then, that considerable quan- 
tities of these animals are destroyed every year, and that the 
unwieldy and awkward on land, where its movements forcibly remind the spectator 
of the wrigglings of a gentle or fly -maggot ; hut it makes considerable use of its 
hind-legs, by bringing them forward and thus taking hold of the ground ; whereas, 
those of the Seals are more directed backwards. When in the water, and about 
to dive, both the Walrus and the Sea-bears show their hacks above the surface, like 
a Porpoise, but this is never observed of the true Seals. — Ed. 
