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.
