Jerboa is a generic name, which is made use of to denote those
remarkable animals whose legs are extremely disproportionate; those
before being not above one inch long, and those behind two inches one
fourth, exactly resembling those of a bird. There are four distinct
species, or varieties, in this genus; first, the _tarsier_, which we
have already spoken of, and which is certainly a particular species,
having five toes on each foot, like those of a monkey. Secondly, the
_jerboa_, which has four toes on the fore-feet, and three on those
behind. Third, the _alagtaga_, whose feet are formed like those of the
jerboa, with this difference, that it has five toes on the fore-feet,
and three on the hind, with a spur, that may be considered as a thumb,
or fourth toe, much shorter than the others. Fourth, the _daman
Israel_, or _lamb of Israel_, which has four toes to the fore feet, and
five on those behind, and which may possibly be the same animal that
Linnæus has described under the name of _mus longipes_.
The head of the jerboa is sloped somewhat in the manner of a rabbit;
but the eyes are larger, and the ears shorter, higher, and broader in
proportion to its size. Its nose is deprived of hair, and is of a flesh
colour, and its muzzle short and thick, the orifice of the mouth very
narrow, the upper jaw very broad, and the lower narrow and short; the
teeth are like those of a rabbit; the whiskers are composed of long
black and white hairs; the fore feet are very short, and never touch
the ground; they are furnished with four claws, and are only used as
hands to carry the food to the mouth; the hind feet have but three
toes, the middle one is longest, and all of them have claws; the tail
is three times longer than the body, and is covered with short stubborn
hair, of the same colour as those on the back, but tufted at the end
with longer and softer hair; the legs, nose, and ears, are bare, and of
a flesh colour; the upper part of the head and back are covered with
reddish hair, the sides, throat, and belly, are whitish; below the
reins, and near the tail, there is a large black, transversal band, in
the form of a crescent.
The alagtaga is smaller than a rabbit, its body is shorter, its
ears are long, wide, bare, thin, transparent, and sprinkled with
blood-vessels, which are very apparent; the upper jaw is much larger
than the lower, but blunt and pretty wide at the extremity; the
whiskers are large; the teeth are like those of the rat, the eyes full,
with the iris and pupil of a brown colour. The body of this animal is
narrow before, but very broad and round behind; the tail is very long,
it is not so thick as the little finger of a man, and about two-thirds
of it is covered with short and rough hair, which grows longer, softer,
and thicker, towards the end, till at length it forms a kind of tuft,
black at the beginning, and white towards the extremity. The fore-feet
are very short and have five toes, the hind ones, which are very long,
have only four, three of which are placed forwards, and the fourth,
which is a kind of thumb, stands at about an inch distant from the
rest. All these toes are furnished with claws, shorter in the hind than
in the fore-feet. The hair of this animal is soft, pretty long, yellow
on the back, and whitish under the belly.
By comparing these two descriptions, the first of which is taken from
Edwards and Hasselquist, and the second from Gmelin, we shall perceive,
that these animals resemble each other as much as possible. The jerboa
is only smaller than the alagtaga, and has only four toes on the
fore-feet, and three on the hind ones, without any spur; while the
other has five on the fore-feet, and three and a spur on those behind;
but I am inclined to think this difference is not universal, for Dr.
Shaw, who has given a description of the jerboa of Barbary, represents
it with this spur, or fourth toe, on the hind-feet; and Mr. Edwards
remarks, that he carefully examined two jerboas he saw in England,
and that he saw no spur in either of them. Thus this character which
would specifically distinguish the jerboa from the alagtaga, not being
universal is of no consequence, and rather remarks the identity, than
the diversity of the species. Neither is the difference of size any
greater proof of their being two different species; possibly Edwards
and Hasselquist have only described young jerboas, and M. Gmelin, an
old alagtaga. There are only two things which create any doubt in my
mind, viz. the difference in the size of their tails, and the variety
in the climates they inhabit, for the jerboa is common in Circassia,
Egypt, Barbary, and Arabia; and the alagtaga, in Tartary, along the
Wolga, and as far as Siberia. It is seldom that the same kind of animal
inhabits such different climates; and whenever it does happen the
species undergoes great changes; which, we presume, is the case with
the jerboa, of which the alagtaga, notwithstanding these differences,
seems to be only a variety.
These little animals commonly conceal their hands, or fore-feet, among
their hair; so that at first they appear to have only hind-feet.
When they move from one place to another, they do not walk, that is
advance one foot before the other, but jump or bound with the greatest
ease, four or five feet at a time; they rest themselves in a kneeling
posture, and only sleep in the day. In the night they seek for food,
like hares, and like them, feed on grass and all kinds of grain. They
are of a gentle nature, but are not to be tamed beyond a certain limit.
They burrow like rabbits, and in much less time. They lay up a store of
grass towards the end of summer in their habitations, and in which, in
cold countries, they remain during the winter.
With respect to the daman, or lamb of Israel, which seems to be of
the jerboa kind, as its fore-legs are much shorter than those behind,
having never seen it, we cannot do better than copy the description
of it as given by Dr. Shaw, who speaks of these two animals as of
different kinds: "The daman (says this author) is also a native of
Mount Lebanon, and common to be met with in Syria and Phoenicia; it is
a very harmless animal, resembling the common rabbit in size, shape,
and also in the disposition of the fore-teeth; but it is somewhat
browner, has smaller eyes, and a head more pointed. Its fore-feet are
short, and those behind long, much in the same proportion as those of
the jerboa. Although it sometimes conceals itself in the earth, its
common retreat is in the hollows and clefts of rocks, which is a strong
reason to conclude that it is this animal and not the jerboa, which
is meant in Scripture by the _Saphan_. I have not been able to learn
from any one why it was called the _daman_ of Israel, which signifies
the _lamb_ of Israel." Prosper Alpinus, who mentioned this animal
before Dr. Shaw, says, that its flesh is delicate food, and that it is
much bigger than the European rabbit; but this last circumstance seems
doubtful, for Dr. Shaw has omitted this passage of Prosper Alpinus,
whom, in other respects, he has fully quoted.