These two animals have had the name of _Sloths_ given to them on
account of their slowness, and the difficulty with which they walk.
Though they resemble each other in many respects, nevertheless they
differ externally and internally by such strong characters that it is
impossible to mistake the one for the other, or doubt of their being
very distinct species. The unau (_fig. 166._) has no tail, and only
two claws on the fore feet. The aï has a short tail, and three claws
on each foot. The nose of the unau is likewise longer, the forehead
higher, and the ears larger than the aï. They differ also in the hair.
Some parts of their viscera are formed and situated different; but the
most distinct and singular character is, the unau has forty-six ribs;
and the aï but twenty-eight; this alone proves them to be two species
quite distinct from each other. These forty-six ribs in an animal whose
body is so short is a kind of excess, or error, in nature; for even
in the largest animals, and those whose bodies are relatively longer
than they are thick, not one of them is found to have so many; the
elephant has only forty, the horse thirty-six, the badger thirty, the
dog twenty-six, the human species twenty-four, &c. This difference
in the construction of the sloths supposes a greater dissimilitude
between these two species than there is between the cat and dog, both
of which have the same number of ribs. External differences are nothing
in comparison with internal ones. The internal frame of living animals
is the groundwork of Nature's design, it is the constituent form, and
the cause of all figure; and the external parts are only the surface
or drapery. In our comparative examination of animals, how many have
we seen who often differed very much in their outward appearance and
yet were perfectly alike internally; and, on the contrary, the least
internal distinction has produced great external differences, and even
changed the natural habits, faculties, and attributes of the animal?
How many also are there armed, cloathed, and even ornamented with
superfluous parts, which, nevertheless, in their internal organization
entirely resemble others who are deficient in these excrescences? but
we shall not here dwell on this subject, which supposes, not only
a reflected comparison, but also an exposition of all the parts of
organization; we shall only observe, that in proportion as Nature
is lively, active, and exalted in the ape species, she is slow,
constrained, and cramped in the sloths. These animals have neither
incisive nor canine teeth; their eyes are dull, and almost concealed
with hair; their mouths are wide, and their lips thick and heavy;
their fur is coarse, and looks like dried grass; their thighs seem
almost disjointed from the haunches; their legs very short and badly
shaped; they have no soles to their feet, nor toes separately moveable,
but only two or three claws excessively long and crooked downwards,
which move together, and are only useful to the animal in climbing.
Slowness, stupidity, and even habitual pain, result from its uncouth
conformation. They have no arms either to attack or defend themselves;
nor are they furnished with any means of security, as they can neither
scratch up the earth nor seek for safety by flight, but confined to
a small spot of ground, or to the tree under which they are brought
forth, they remain prisoners in the midst of an extended space, unable
to move more than three feet in an hour; they climb with difficulty and
pain; and their plaintive and interrupted cry they dare only utter by
night. All these circumstances announce their wretchedness, and call
to our mind those imperfect sketches of Nature, which, having scarcely
the power to exist, only remained a short time in the world, and then
were effaced from the list of beings. In fact, if it were not a desart
country where the sloths exist, but had been long inhabited by man
and powerful animals, they would not have descended to our time; the
whole species would have been destroyed, as at some future period will
certainly be the case. We have already observed, that it seems as if
all that _could_ be, _does_ exist; and of this the sloths appear to be
a striking proof. They constitute the last term of existence in the
order of animals endowed with flesh and blood. One more defect and
they could not have existed. To look on these unfinished creatures as
equally perfect beings with others; to admit final causes for such
disparities, and from thence to determine Nature to be as brilliant
in these as in her most beautiful animals, is only looking at her
through a straight tube, and making its confines the final limit of our
judgment.
Why should not some animals be created for wretchedness, since in the
human species the greatest number are devoted to pain and misery from
their birth? Certainly, evil is more our own production than that of
Nature. For one man who is unhappy from being born weak and deformed,
thousands are rendered so by the oppression and cruelty of their
fellow-creatures. Animals are, in general, more happy, because each
species has nothing to dread from their individuals; to them there is
but one source of evil, but to the human species there are two. Moral
evil, which he has produced himself, is a torrent which is increased
into a sea, whose inundation covers and afflicts the whole face of
the earth. Physical evil, on the contrary, is confined to very narrow
limits; it seldom appears alone or unaccompanied with an equal if not a
superior good. Can animals be denied happiness when they enjoy freedom,
and have the faculty of easily procuring subsistence, when they are
less subject to ill health, and possess the necessary or relative
organs of pleasure in a more eminent degree than the human species?
In these respects animals in general are very richly endowed; and the
degraded species of the sloths are, perhaps, the only creatures to
whom Nature has been unkind, and the only ones which present us the
image of innate misery and wretchedness.
Let us now inspect their condition more closely; being unfurnished with
teeth they cannot seize upon prey, nor feed upon flesh or vegetables;
reduced to live on leaves and wild fruits, they consume much time in
crawling to a tree, and still more in climbing up to the branches;
and during this slow and painful labour, which sometimes lasts many
days, they are obliged to support the most pressing hunger. When they
have accomplished their end they cling to the tree, crawl from branch
to branch, and, by degrees, strip every twig of its leaves. In this
situation they remain several weeks without any liquid; and when they
have consumed the store, and the tree is entirely naked, they still
continue, unable to descend until the pressure of hunger becomes more
powerful than the fear of danger or death, and they suffer themselves
to fall to the ground like an inanimate mass, without being capable of
exerting any effort to break the violence of the fall.
When on the ground they are exposed to all their enemies, and as their
flesh is not absolutely bad they are sought after both by men and
beasts of prey. They seem to multiply but little, or if they produce
often it is only a small number at a time, as they are furnished with
but two teats: every thing, therefore, concurs to their destruction,
and the species supports itself with great difficulty. Although they
are slow, heavy, and almost incapable of motion, yet they are hardy,
strong, and tenacious of life; they can exist a long time deprived of
all food; they are covered with a thick, coarse fur, and being unable
to take much exercise they waste little by perspiration, and therefore
they fatten by rest, however poor their food. Though they have neither
horns nor hoofs, nor incisive teeth in the lower jaw, they belong,
notwithstanding, to the number of ruminating animals, and have four
stomachs, so that they may compensate for the quality of their food
by the quantity they take at a time; and what is still more singular,
instead of having, like other ruminating animals, very long intestines,
they are very short, like those of the carnivorous kind. The ambiguity
of Nature seems somewhat discovered by this contrast. The sloths are
certainly ruminating animals, as they have four stomachs; but they
are deficient in all the other external and internal characters which
belong to all animals in that class. There is also another singularity
in these animals, instead of distinct apertures for the discharge of
the urine, excrements, and the purposes of generation, these animals
have but one, which terminates in a common canal, as in birds.
Finally, if the misery which results from a defect of sensation be not
the greatest of all, the miserable state of these animals, although
very apparent, seems not to be real, for they appear to have little
or no sensation, and their dull and heavy look, their indifference to
blows, which they receive without being in the least affected, prove
their insensibility. But what still further demonstrates this fact is,
their not instantly dying upon their hearts and bowels being taken out.
Piso, who made this cruel experiment, says, that the heart, after being
separated from the body, beat forcibly for more than half an hour, and
that the animal continued to contract its limbs in the same manner as
when asleep.[AM] From these circumstances this quadruped approaches not
only the tortoise but also other reptiles who have no distinct centre
of sensation: thus all these animals are miserable without being
unhappy; and Nature, even in her most unfinished productions, appears
always to act more as a real parent, than a step-mother.
[AM] Sonnini says, that wishing to kill a sloth for the purpose of
preparing the skin, he exhausted every possible means to deprive it
of life; but such was its principle of vitality that he could not
remain any longer a witness of his own barbarous endeavours; and he
quitted the room seized with horror at the idea of the evils which
this miserable animal must endure, and with astonishment at that
impenetrability which prolonged its existence.
Both these animals belong to the southern parts of the New Continent,
and are never to be met with in the Old. We have already observed,
that the editor of Seba's cabinet was deceived in calling the unau by
the name of the _Ceylon sloth_. This error, which has been adopted by
Klein, Linnæus, and Brisson, is now more evident than formerly. The
Marquis de Montmirail has a living unau, which was brought him from
Surinam: those in the royal cabinet came from the same place, and from
Guiana; and I am persuaded, that both species exist in the desarts
of America, from Brasil to Mexico; but as it never inhabited the
northern countries, it could not have passed from one continent to the
other; and if these animals have been seen either in the East Indies,
or on the coast of Africa, it is certain, that they must have been
transported thither. They can endure neither cold nor rain; the change
from wet to dry spoils their fur, which then resembles bad dressed
hemp, rather than wool or hair.
I cannot conclude this article better than by inserting the
observations which the Marquis de Montmirail communicated to me
concerning the unau, which had been above three years in his menagerie.
"The fur of the unau is much softer than that of the aï. It is probable
that what travellers have said of the excessive slowness of the sloths,
only belongs to the aï. The unau, although very heavy, and of an
excessively aukward motion, ascends and descends the highest tree many
times in a day: he is most active in the evening and during the night,
which makes it probable that he sees but badly in the day, and that his
eyes are of no use to him but in the dark. When I bought this animal
at Amsterdam, it was fed with sea-biscuit, and I was told, that when
the winter was over, and the verdure began to appear, it would require
nothing but leaves. We supplied him with leaves which he ate freely
while they were green and tender; but the moment they began to be dry,
shrivelled, or worm-eaten, he refused them. During the three years that
I preserved him in my menagerie, his common food was bread, apples,
and roots; and his drink always milk. He always took his food in one
of his fore-claws, but with difficulty, and which was increased in
proportion to the size. His cry, though plaintive and melancholy, does
not resemble that of the aï; it is short, and seldom uttered. The most
natural situation of the unau, and which he prefers to all others, is
suspending himself on a branch of a tree, with his body downwards. He
sometimes even sleeps in this position, his four claws fastened on the
same point, and his body describing the figure of a bow. The strength
of his muscles is incredible; but it becomes useless to him when he
walks, for his motion then is not the less constrained or tottering.
This formation alone seems to be the cause of the slowness of this
animal, who besides has no violent sensation, and does not recognize
the hand that feeds him."