CHAPTER III.. Mole Rats, Pouched Rats, Pouched Mice, Jerboas, and Octodontidæ.

MOLE RATS, POUCHED RATS, POUCHED MICE, JERBOAS, AND OCTODONTIDÆ.

SPALACIDÆ, OR MOLE RATS--Characteristics of the Family--Habits--Food--THE MOLE RAT--Distribution--Description--THE CHESTNUT MOLE RAT--THE NAKED MOLE RAT--THE STRAND MOLE RAT--Description--Habits--THE CAPE MOLE RAT--GEOMYIDÆ, OR POUCHED RATS--Characteristics of the Family--The Cheek-pouches--THE COMMON POCKET GOPHER--Distribution--Description--Burrowing--Runs--Subterranean Dwelling--THE NORTHERN POCKET GOPHER--HETEROMYINÆ, OR POUCHED MICE--Difficulties as to Position--Characteristics--PHILLIPS’ POCKET MOUSE--Where Found--Description--THE YELLOW POCKET MOUSE--THE LEAST POCKET MOUSE--DIPODIDÆ, OR JERBOAS--Organisation for Jumping--Characteristics--Distribution--THE AMERICAN JUMPING MOUSE--Description--Characters peculiar to itself--Habits--THE TRUE JERBOAS--Characters--THE JERBOA--Distribution--Habits--Mode of Locomotion--THE ALACTAGA--THE CAPE JUMPING HARE--THE PORCUPINE-LIKE RODENTS--OCTODONTIDÆ--Characteristics--Sub-Family, CTENODACTYLINÆ--THE GUNDI--THE DEGU--Description--Habits--THE BROWN SCHIZODON--THE TUKOTUKO--THE CURURO--THE ROCK RAT--Sub-Family, ECHINOMYINÆ--THE COYPU--One of the Largest Rodents--Description--Burrows--Habits--Mother and Young--THE HUTIA CONGA--THE HUTIA CARABALI--THE GROUND RAT.

FAMILY VIII.--SPALACIDÆ (MOLE RATS).

Although the Zokor and its allies in the preceding family have to a certain extent prepared us for the peculiar characters presented by the Mole-rats, these are exhibited by the latter in a much more extreme form. They have a very large broad head, which is usually flattened above, and forms an appropriate anterior termination to a clumsy, cylindrical body, supported upon short stout limbs; their incisor teeth are large and broad, and are most formidably exposed in front of the mouth; their eyes are exceedingly small, hidden in the fur, and sometimes quite rudimentary; the external ears are reduced to the smallest possible size, or altogether wanting; and their tails are either so short as to be concealed within the hair of the hinder part of the body, or altogether wanting externally, although the skeleton still shows some caudal vertebræ. The molar teeth are rooted, and not tuberculate; their surface shows re-entering folds of enamel. The feet have five toes, but the thumb is generally very small, although furnished with a nail. The number of molars varies from three to six on each side in each jaw.

In their mode of life, as in their form and the condition of the organs of sight and hearing, these animals present a considerable resemblance to the Moles; but as their food is exclusively of a vegetable nature, the object of their burrowing is not exactly the same. They all inhabit the eastern hemisphere, and are generally met with in dry sandy plains, the soil of which lends itself readily to mining operations. They seldom quit their burrows, and usually work in these only at night, when they make their way rapidly through the ground, and, like the Mole, can run either backwards or forwards in their subterranean galleries with equal facility. They feed chiefly on roots, and especially on the bulbs and tubers which so many plants possess in the dry districts which they frequent; but some of them also eat nuts, seeds, the young bark of trees, and herbage. None of them fall into a state of torpidity during the winter--indeed, only two species inhabit northern regions; but these, although active in the winter season, are said not to take the precaution to lay up a store of provisions.

Most zoologists distinguish two groups of Spalacidæ. In the SPALACINÆ, the representatives of which range from south-eastern Europe to further India and the south of China, and also occur in Africa in the countries of Abyssinia and Shoa, the palate between the molar teeth is broader than one of the sockets of the molars, and the angular portion of the lower jaw springs from the lower edge of the bony case of the incisor. To this group belongs the MOLE-RAT (Spalax typhlus), which inhabits Hungary and Galicia, and the south-east of Europe generally, and ranges eastwards into Asia as far as the Caucasus and Ekaterinoslav. It possesses only three molars on each side in each jaw, and has the eyes rudimentary and covered by the skin, so that the animal is quite blind; the upper incisors are placed perpendicularly; and the tail reduced to a sort of wart. The toes, especially those of the fore-feet, are furnished with very powerful claws, which are vigorously employed by the animal in the digging operations above described. The general covering of the body is a soft fur of a yellowish-brown colour, tinged with ashy-grey; the head lighter, but becoming brownish behind; and the lower surface ashy-grey, with some white streaks and spots. The muzzle, chin, and feet are whitish, and along each side of the face there runs a sort of ridge of stiff bristle-like hairs. This species is particularly abundant in the Ukraine and the country about the Volga and the Don.

The genus Rhizomys, of which there are an East Indian and two African species known, has the eyes uncovered, though very small, short naked ears, and a short partially hairy tail. The upper incisors are arched forward. The CHESTNUT MOLE-RAT (Rhizomys badius) lives in Northern India, Siam, and Arracan; and, according to Mr. Finlayson, the food of a specimen in confinement consisted of unhusked rice and other grain, but he showed himself fond of yams and pumpkins. The NAKED MOLE-RAT (Heterocephalus glaber), which has no external ears and a short tail, has the body almost entirely naked. It is a native of Shoa.

The other section of the Mole rat family, the BATHYERGINÆ, is entirely confined to Africa, and, indeed, almost exclusively to the southern extremity of that continent, only a single species being found elsewhere--at Mozambique. They show a resemblance to the Hystricine Rodents in the structure of the lower jaw, the angular portion of which springs from the side of the bony case of the lower incisor; and the palate between the molars is narrower than in the Spalacinæ. The best known of the six species inhabiting the Cape of Good Hope is the STRAND MOLE-RAT (Bathyergus maritimus), which is nearly as large as a small Rabbit, its length being about ten inches, with a tail two inches in length. In general form it resembles the species last described; it has small but uncovered eyes, a broad nose, no external ears; very long, compressed, and powerful claws on all the toes, except the thumb of the fore-feet, which has a crooked nail; four molars on each side, and long white incisors, of which the upper ones are strongly grooved in front. The colour of the fur is greyish-white, with a yellowish tint on the upper surface. The tail has a sort of radiating tuft of hairs at the end. The Strand Mole-rat lives entirely in sandy localities near the sea-shore, and especially in the sand-hills or dunes which fringe the coast of the Cape of Good Hope in some parts. Here it burrows freely in all directions, its galleries generally radiating from several central points, and joining in various places. It avoids the light as much as possible, and if by chance it is exposed on the surface it is exceedingly helpless. Very little is known of the habits of this species, which probably feeds chiefly on roots like the other members of the family. It is regarded as mischievous, as it undermines the ground so much as to make it unsafe to ride over. The colonists, therefore, often destroy it by various means. The enamel folds of the teeth become effaced with use.

The Georychi, five species of which inhabit Cape Colony, resemble the preceding species, but are smaller and weaker. The claws of the fore-feet are shorter and weaker, and the upper incisors, which are long and arched forward, are not grooved. The best-known species is the so-called CAPE MOLE-RAT (Georychus capensis). In the Mozambique species (Heliophobius argenteo-cinereus) there are six molars on each side above and below, and the second toe of the hind feet is the longest. In most other characters it resembles Georychus.

FAMILY IX.--GEOMYIDÆ, OR POUCHED RATS.

The Pouched Rats, or Pocket Gophers, and the Pouched Mice of North America, constitute a family distinguished from all the preceding forms by the presence of a pair of great cheek-pouches, opening outside and not inside the mouth (see figure). These cheek-pouches are hairy inside throughout. The angular portion of the lower jaw is strongly twisted, the molars are four in number on each side in each jaw, and the squamosal bone is very large. In external characters the animals of this family present considerable diversity, which has led to their being divided into two well-marked sub-families, the distinctive peculiarities of which are of such importance that Dr. Coues has raised them to the rank of distinct families. The GEOMYINÆ, or Pouched Rats, are more or less Rat-like animals, in which the feet are five-toed, and all the toes furnished with claws, those of the fore feet being very strongly developed; and the tail is short. Certain other characters are presented by the skull. The outline of this part, including the zygomatic arches, is almost quadrangular; the infra-orbital opening is far in front of the jugal process; the malar bone extends forward to the lachrymal.

Of the animals thus characterised, the Continent of North America possesses, according to Dr. Coues, seven species, and they are met with from Hudson’s Bay and the Columbia River in the north, as far south as Mexico. The best-known species, the COMMON POCKET GOPHER (Geomys bursarius), inhabits the whole valley of the Mississippi, and extends northwards into Canada. It reaches the foot of the Rocky Mountains in Colorado, but is not known to occur west of that range. It is also found in Texas. This Pouched Rat, like the rest of its genus, has the incisors broad and the upper ones deeply grooved; but in addition to the ordinary deep groove it has a fine line close to the inner margin of each of these teeth. Its form is stout and clumsy, but its coat is beautifully soft and velvety, like that of the Mole, but of a dull reddish-brown colour, with the feet and tail white. The average length of an adult specimen is from seven to eight inches, and the tail is two or three inches long. This organ is clothed with hair nearly to the tip.

Like the Mole, this animal lives in burrows, which it makes in all directions in the ground, throwing out as it proceeds heaps of earth, which exactly resemble ordinary mole-hills. To enable it to perform these labours the claws of the fore feet are exceedingly powerful; and to adapt it the better to its subterranean existence, the eyes are very small, and the external ears are wanting. Its digging operations have generally the same object as those of the Mole--namely, the search for food. The tunnel is carried along not far from the surface of the ground, and the roots of any plants that lie in its course are bitten off and devoured by the little miner. Besides the runs, the Pouched Rat digs himself a convenient dwelling in the shape of a chamber hollowed out under the roots of a tree, access to which is gained by a somewhat spiral descending passage. This chamber, which is usually at a depth of four or five feet, is comfortably lined with soft grass, and the nest in which the female brings forth her young is a cavity of the same kind, but surrounded by circular passages, from which, like that of the Mole, other passages branch off. One of these, according to Gesner, leads from the nest to a large store-chamber filled with nuts, seeds, and roots, among which the potato was found to play an important part. These provisions are carried to the store-house in the great cheek-pouches, which the animal is said to fill by the aid of its tongue, and to empty with the fore paws. This Pouched Rat does much damage in cultivated ground by attacking the roots of both plants and trees, sometimes destroying a great number of the latter in a few days. The female produces from five to seven young at the end of March or the beginning of April. The other species of Geomys closely resemble this in their habits.

Of the second genus belonging to this sub-family (Thomomys) Dr. Coues admits only two species, one of which, however, occurs under three named forms. They may be distinguished from the species of Geomys by their having the upper incisors plain, without grooves.

The NORTHERN POCKET GOPHER (Thomomys talpoides), with its sub-species, ranges over nearly the whole of North America from the Hudson’s Bay Territory to California and New Mexico. The three forms are for the most part in accordance with geographical distribution. A small species (Thomomys clusius) has been obtained in the Rocky Mountains.

The HETEROMYINÆ (forming the family Saccomyidæ of Dr. Coues, although he does not accept the genus Saccomys) are more slender and delicate in form than the Geomyinæ, and have the hind limbs and tail elongated, the former, indeed, being converted into leaping organs like those of the Jerboas and Kangaroos. The eyes and ears are larger, and the animals are in every respect adapted to life in the open, while the Geomyinæ, on the contrary, are subterranean in their habits. The hair in the present family is coarse and harsh, sometimes even spiny. In skeletal characters we find a similar alteration. The incisors are narrow; the skull is delicate, with its angles rounded off, and the mastoid bones form a considerable part of the roof of the cranial cavity; the zygomatic arches are slender; and, the lower root of the maxillary process being undeveloped, the infra-orbital opening is not defined. As in the Jerboas, the cervical vertebræ are sometimes anchylosed. Like the Geomyinæ, these animals are confined to America, and chiefly limited to the Southern United States and Central America, although some of the species occur as far north as the Columbia River and Hudson’s Bay, and one is found in Trinidad. By American writers they are called “Pocket Mice.”

PHILLIPS’S POCKET MOUSE, also known as the Kangaroo Rat (Dipodomys Phillipsii), is one of the best known species of this group. It is an elegantly formed little creature, about four inches long, with a slender tail nearly six inches in length. Its colour above is mouse-brown, white beneath; the sides of the body have some white streaks, especially one from the ear towards the shoulder, and one on the thigh running towards the root of the tail; the tip of the tail is also white. This is a Californian species, but extends throughout the Pacific region of the United States. It is represented in the Rocky Mountains by a rather larger and stouter form, with smaller ears and a shorter tail (Dipodomys Ordii), which is generally regarded as distinct, but is placed by Dr. Coues as a sub-species. The habits of the species are comparatively little known, but they appear to live in the most desert places they can find, the barren spots on which the only plants that seem to flourish are the great mis-shapen cactuses. They dwell in holes under rocks and stones, from which they emerge at sunset, and hop about gaily after the fashion of little Kangaroos. The places in which these Pocket Mice are found are so bare of vegetation and destitute of water, that it is difficult to imagine how they contrive to exist. In all probability they pick up a scanty living in the shape of roots and grasses, especially seeds, carrying a supply for the day into their holes in their great cheek-pouches.

The YELLOW POCKET MOUSE and the LEAST POCKET MOUSE (Cricetodipus flavus and parvus) are very minute creatures, only about two inches long in the head and body. The tail is longer than the head and body in the latter, shorter in the former species, and the colour of the fur in both is a pale buff. These species are found in the Rocky Mountains and the region west of that range to the Pacific, the latter being inhabited by the second of the above species. Several species of the genus Heteromys inhabit Central America, and one is found in the island of Trinidad. Nothing appears to be known of their habits.

From these we pass as by a natural transition to

FAMILY X.--DIPODIDÆ (THE JERBOAS).

The JERBOAS are a more extensive and much more widely distributed family of hopping Rodents. In these we find the organisation for jumping brought to greater perfection than in any other group. The body is light and slender, the hind limbs much elongated, the fore limbs very small, and the tail long and usually tufted at the end. The number of toes on the hind feet varies from three to five, and the metatarsal bones are very often united so as to form what is called a “cannon bone” in the Horse. The incisor teeth are compressed; the molars sometimes four, but usually three in each series, rooted or rootless, not tuberculate; the infra-orbital opening is rounded and very large, and the zygomatic arch slender. The great home of these animals is the vast steppe region which stretches from South-eastern Europe across the greater part of Central Asia, but they extend southwards round the eastern extremity of the Mediterranean, through Syria and Arabia to Egypt and Africa, over a great part of which they are found, and eastward to India, Afghanistan, and Ceylon. A single species occurs at the Cape of Good Hope; and another is found in North America. We may commence by noticing this last species, as it not only makes the nearest approach to those of preceding families, especially the Muridæ, but differs from the rest of the Jerboas in characters of such importance, that Dr. Coues maintains its right to form a separate family (Zapodidæ).

The AMERICAN JUMPING MOUSE (Zapus hudsonius) has a wide range, extending across the continent of North America from sea to sea, and from Labrador, Hudson’s Bay, and the Great Slave Lake in the north, to Virginia and the elevated portions of Arizona and New Mexico in the south. It is an elegant little mouse-like creature, rather more than three inches long, and furnished with a cylindrical tail, which exceeds the head and body in length by about two inches. Its hind limbs are not quite so disproportionately developed as in the other members of the family. Its fur in summer is of a brown colour above, becoming yellowish on the sides and white below; in the winter the brown tint covers the whole surface. The ears, which are not very large, are black, with a light-coloured rim; the hind feet are greyish, and the fore feet whitish on the upper surface; and the tail, which tapers to an exceedingly fine point, where there is a fine pencil of hairs, is ringed and nearly naked.

The characters in which this animal differs from its nearest relatives are as follows:--In the upper jaw there are four rooted molars on each side, the first being very small, the second the largest, and the rest gradually diminishing in size; the fore feet have the thumbs rudimentary, and the hind feet have five toes, all of which touch the ground; the metatarsal bones are separate; and the soles of the feet naked, with granules and small horny shields.

The American Jumping Mouse is found in meadows in the neighbourhood of woods and copses. It is nocturnal in its activity, sleeping during the day in its burrow, which is usually about two feet deep, and coming forth at night. It is sociable in its habits, and excessively active, covering from three to five feet of ground at each leap, so that it is a matter of no little difficulty to capture a specimen in the open. In the woods it is worse, as the little creature will bound over bushes, and get out of sight in a moment. Its food consists of seeds of various kinds, and it is exceedingly fond of beech-mast. For protection from the cold of winter the Jumping Mouse makes a little hollow clay ball, within which it coils itself up, and goes comfortably to sleep. The nest is made about six inches under the surface of the ground, and is composed of fine grass, sometimes mixed with feathers, wool, and hair; and in this the female produces from two to four young, probably several times in the course of the summer, as the nests and young are to be found from May to August.

If we regard the American Jumping Mouse as constituting a peculiar section of the family, ZAPODINÆ, a second group, DIPODINÆ, is formed by the TRUE JERBOAS, which make up the greater part of the family. These either possess only three molars, or a very small additional tooth exists in front of each series in the upper jaw. The molars are rooted, and diminish in size backwards in each series. The cervical vertebræ are anchylosed; the fore feet have the thumbs rudimentary, but sometimes furnished with a small nail; the hind feet have only three toes fully developed, and the metatarsals are united into a single bone of great length; the soles are furnished with elastic balls; and the tail is very long, well-clothed with hair, and tufted at the end.

Of these pretty little creatures, which are in some respects singularly bird-like, about twenty species have been recorded, and these occupy the whole of the Old World area of the family, except South Africa. The JERBOA (Dipus ægyptius) may serve as an example of this section of the family. This is a most lively and active little creature, which inhabits the deserts of north-eastern Africa as far south as Nubia, and extends its range into Arabia and south-western Asia. On these arid plains, so scantily clothed with a few grasses and dry shrubs that it is difficult to conceive how any animal can find a living on them, the Jerboa lives, often in numerous societies, and in company with the few birds and lizards which enliven the wilderness. These animals dwell in subterranean abodes consisting of many branched galleries, which they dig out in the hard soil not far from the surface. The Arabs assert that these habitations are produced by the joint labour of the whole society. They retreat into their burrows at the least alarm. The females are said to produce from two to four young at a birth in a nest made in the deeper part of the burrow, and lined with hair pulled from the under surface of her own body. When going along quietly, the Jerboa walks and runs by alternate steps of the hind feet, but when there is occasion for rapid motion it springs from both feet at the same time, covering so much ground at each leap, and touching the ground so momentarily between them, that its motion is more like that of a bird skimming close to the surface of the ground than that of a four-footed beast.

The Jerboa is about six inches long, with a tail about eight inches in length exclusive of the tuft with which its tip is adorned. Its upper surface is of a greyish sand-colour, like that of many other desert animals; the lower surface is white; and the tail pale-yellowish above and white beneath, with the tuft white, with an arrow-shaped black mark on its upper surface.

Several other species of Jerboas are known, some from the deserts of North Africa, others from the steppes of Central Asia. The latter region harbours some forms, which differ from the preceding, among other characters, by having five toes in the hind feet, whereas the true Jerboas have only three, but of the five toes only three are sufficiently developed to take part in the animal’s progression. The best known of them is the ALACTAGA (Alactaga jaculus), a rather larger species than the Jerboa, and with a still longer tail, reddish-yellow with a greyish tinge above, white beneath and on the hind legs. Its range extends from the Crimea and the steppes of the Don across Central Asia to the borders of China. It walks upon all-fours, and when advancing quickly springs along after the fashion of the Jerboa. Its food consists of all sorts of vegetable substances, but it is especially fond of the bulbs of plants, and does not refuse occasionally to eat insects, or even the eggs and young of the birds which inhabit the steppes with it. The Alactagas live in very complicated burrows, with many passages and branches, and they are said always to make one passage from the central chamber of their residence, which terminates close to the surface of the earth at some distance, but is only opened in case of danger, when the inhabitants escape through it, the position of its intended aperture being previously unrecognisable. In cold weather they sleep in their nests. The female produces from five or six to eight young, in a nest lined with her own hair. Species of Alactaga occur not only in Central Asia, but also in Arabia and North Africa.

South Africa produces one species, the CAPE JUMPING HARE (Pedetes caffer), which constitutes a distinct sub-family, PEDETINÆ, having four rootless molars on each side in each jaw, the metatarsal bones separate, the tail bushy, and the hind feet furnished with four toes having broad, hoof-like nails. This is a much larger animal than any of the preceding, being about the size of the common Hare, which it also resembles in its colours. The Jumping Hare inhabits a considerable portion of South Africa, extending on the west coast at least as far as Angola. It is abundant at the Cape of Good Hope, both in the mountains and in the plains. Great numbers of the animals often live together, and their burrows, which, like those of other Dipodidæ, are inhabited by numerous individuals as a common residence, consist of many-branched galleries made at no great depth from the surface, but leading into a more deeply-seated habitation. They generally go about slowly upon all-fours, but can advance with extraordinary rapidity by Kangaroo-like springs, in each of which, when pressed, they will cover a space of twenty or thirty feet. Their food consists of roots, seeds, and herbage. The female produces three or four young at a birth.