CHAPTER X

THE ORDER RODENTIA

The Rodentia, or Rodents, form a well-defined order, readily distinguished by their large scalpriform incisors and the absence of any trace of canines. The existing forms are mostly of comparatively small size, and are generally of terrestrial habits, although a few are arboreal or natatorial. The dentition is diphyodont; the mandible never has more than a single pair of incisors; the premolars are always below the full number, being very generally ¹⁄₁, or altogether wanting. The feet are plantigrade or semi-plantigrade, generally with five digits, and usually unguiculate, although occasionally of a subungulate type. Clavicles are present as a rule, although they may be imperfect or rudimentary.

The upper incisors resemble the lower in growing uninterruptedly from persistent pulps, and, except in the suborder Duplicidentata, agree with them in number; the premolars and molars may be rooted or rootless, with tuberculated or laminated crowns, and are arranged in an unbroken series. The orbits communicate freely with the temporal fossæ; the condyle of the mandible is elongated in the antero-posterior direction, and, through the absence of a post-glenoid process to the squamosal, admits of a backward and forward motion of the jaw. The intestine (except in the _Myoxidæ_) has a large cæcum; the testes are inguinal or abdominal; the uterus is two-horned, the cornua either opening separately into the vagina or uniting to form a corpus uteri; the placenta is discoidal and deciduate; and the smooth cerebral hemispheres do not extend backwards so as to cover any part of the cerebellum.

[Illustration: FIG. 194.—Skull of _Hystrix cristata_ (juv.) _t_, Temporal muscle; _m_, masseter; _m′_, portion of masseter transmitted through the infraorbital foramen, the superior maxillary nerve passing outwards between it and the maxillary bone.]

The Rodents include by far the greatest number of species, and have the widest distribution of any of the orders of terrestrial mammals, being in fact cosmopolitan, although more abundant in some parts than in others. The total number of known existing species exceeds 900. South America may be regarded as their headquarters at the present day; while in Australia and Madagascar they are represented only by a few genera. All the Rodents are exclusively herbivorous, and the whole of them gather their food by gnawing. They present considerable diversity of habits. Thus the Squirrels are arboreal, and some of them provided with a parachute for taking flying leaps from tree to tree; the Hares are cursorial; the Jerboas agile jumpers; the Mole-Rats fossorial; while the Beavers and Water-Voles are aquatic. In spite, however, of this diversity of habits the Rodents present a remarkable similarity in general structure; so much so, indeed, that the characters employed for distinguishing the various families and genera are comparatively trivial, and of slight structural importance. The skull of the Rodents is characterised by the invariable presence of the zygomatic arch, of which the middle portion is formed by the jugal (Fig. 7, p. 37); and, as already mentioned, the orbit communicates freely with the temporal fossa. There is invariably a long diastema separating the incisors from the cheek-teeth; and, with the exception of the Duplicidentata, the glenoid cavity of the squamosal is elongated antero-posteriorly. Postorbital processes of the frontals exist only in the Squirrels, Marmots, and Hares; in all other genera they are rudimentary or altogether absent; the zygoma never sends upwards a corresponding process; the lachrymal foramen is always within the orbital margin; in many species the infraorbital foramen is very large (in some as large as the orbit), and transmits part of the great masseter muscle (Fig. 194, _m_), by means of which the jaws are worked. The zygomatic arch varies in its degree of development, and the position of the jugal therein is used as a distinguishing character for grouping the families; the nasals are, with few exceptions, large, and extend far forwards; the parietals are moderate, and there is generally a distinct interparietal. The palate is narrow from before backwards—this being especially pronounced in the Hares, where it is reduced to a mere bridge between the premolars; while in other cases, as in the Mole-Rats (_Bathyerginæ_), it is extremely narrow transversely, its width being less than that of one of the molar teeth. Auditory bullæ are always present, and generally large; in some genera, as in the Gerbilles and Jerboas, there are also supplemental mastoid bullæ forming great hemispherical bony swellings at the back of the skull (see Fig. 7, _Per_); and in these genera, and in the true Hares, the meatus auditorius is tubular and directed upwards and backwards. The mandible is characterised by the abruptly narrowed and rounded symphysial part supporting the large incisors, as well as by the small size of the coronoid process and the great development of the angular portion.

The dental formula varies from _i_ ²⁄₁, _c_ ⁰⁄₀, _p_ ³⁄₂, _m_ ³⁄₃ (total 28) in the Duplicidentata to _i_ ¹⁄₁, _c_ ⁰⁄₀, _p_ ⁰⁄₀, _m_ ²⁄₂ (total 12) in _Hydromys_, _Xeromys_, and one species of _Heterocephalus_; but in the great majority of forms it is very constant, _i_ ¹⁄₁, _c_ ⁰⁄₀, _p_ ⁰⁻¹⁄₀₋₁, _m_ ³⁄₃ being very typical. Only in the Duplicidentata is there a second pair of upper incisors, which are of very small size, and situated immediately behind the large normal pair. This group is also peculiar in that the enamel of the incisors is not confined to their anterior surfaces, but extends partially on to their sides. It is by reason of the thick layer of enamel on their anterior surface and its absence from the posterior surface that the incisors maintain their sharp chisel-like edge, which is so essentially characteristic of the order. Both the upper and the lower incisors are regularly curved—the curvature being somewhat greater in the upper ones—and since they grew continuously from persistent pulps, it is quite evident that should any accident, such as the loss of one of them, or displacement by fracture of the jaw, prevent the regulation of the length by attrition against one another, the unopposed tooth will gradually curve upon itself until a complete circle or more has been formed, the tooth, perhaps, passing during its growth through some part of the animal’s head. The molars, as already mentioned, may be rooted or rootless, tuberculated or laminated; this diversity of structure occurring even in the same family. When there are more than three cheek-teeth those in front of the last three have succeeded milk-teeth, and must therefore be considered premolars. In some species, as in the Agoutis (_Dasyproctidæ_), the milk-teeth are long retained, while in the allied Cavies (_Caviidæ_) they are shed before birth.

[Illustration: FIG. 195.—Vertical and longitudinal section through skull of the Beaver (_Castor fiber_) showing the cerebral cavity, the greatly developed turbinal lamellæ, the mode of implantation of the large incisor, and the curved, rootless molars.]

There are generally nineteen dorso-lumbar vertebræ (thirteen dorsal and six lumbar), their form varying in the different genera. In the cursorial and leaping species the lumbar transverse processes are generally very long, and in the Hares there are large compressed hypapophyses. The caudal vertebræ exhibit great variety in structure, being in a rudimentary condition in the Guinea-Pig, while in the Jumping Hares and prehensile-tailed Porcupines they are of very large dimensions. The scapula is usually narrow, with a long acromion; the clavicles may be altogether absent or imperfect, as in the Porcupines, Cavies, and Hares, but in most species they are well developed. In all existing forms the humerus has no entepicondylar foramen, and the radius and ulna are distinct. In most species the manus has five digits, with phalanges normally developed; the pollex being rarely rudimentary or absent. The pelvis has well-developed ischia and pubes, meeting in a long, and usually bony, symphysis. The femur varies considerably in form, but generally has a well-defined third trochanter; in the Sciurine and Hystricine Rodents the tibia and fibula are distinct, but in the Rats and other Murines, and in the Hares, these bones are united, often high up; the pes is much more variable than the manus, the digits varying in number from five, as in the Squirrels and Rats, to four, as in the Hares, or even three, as in the Capybara, Viscacha, and Agouti; in the _Dipodidæ_ the metatarsals are greatly elongated, and in some of the species, as in the Jerboas, they are ankylosed together.

The mouth is divided into two cavities communicating by a constricted orifice, an anterior one containing the large incisors, and a posterior one in which the molars are placed; the hairy integument of the face being continued inwards behind the incisors. This peculiar arrangement evidently prevents substances not intended for food getting into the mouth, as when the animal is engaged in gnawing through an obstacle. In the Hares and Pacas the inside of the cheeks is hairy, and in some species, as in the Pouched Rats and Hamsters, there are large internal cheek-pouches lined with the hairy integument, which open near the angles of the mouth and extend backwards behind the ears. In the New World Pouched Rats (_Geomyidæ_) the pouches open externally on the cheeks. The tongue presents little variability in length, being always short and compressed, with an obtuse apex never protruded beyond the incisors. In most species there are three circumvallate papillæ at the base; and the apical portion is generally covered with small filiform papillæ, some of which in the Porcupines (_Hystrix_) become greatly enlarged, forming toothed spines. The stomach varies in form from the simple oval sac of the Squirrel to the complex ruminant-like organ of the Lemming. In the Water-Vole (_Arvicola amphibius_) and the Agouti (_Dasyprocta aguti_) it is strongly constricted between the œsophagus and pylorus. In the common Dormouse the œsophagus immediately before entering the stomach is much dilated, forming a large egg-shaped sac with thickened glandular walls; and in some other species, as in _Lophiomys imhausi_ and in the Beaver, glandular masses are attached to and open into the cardiac or pyloric pouches. The alimentary canal (Fig. 196) of all Rodents, with the exception of the Dormice (_Myoxidæ_), has a cæcum, which is often of great length and sacculated, as in the Hares, Water-Voles, and Porcupines. In some instances, as in the Hamster and Water-Vole, the long colon is spirally twisted upon itself near its commencement. The liver is typically divided in all, but the lobes are variously subdivided in the different species (in _Capromys_ they are divided into minute lobules); and the gall-bladder, though present in most, is absent in a few. In most species the penis (which is generally provided with a bone) can be more or less completely retracted within the fold of integument surrounding the anus, where it lies curved backwards upon itself under cover of the integument. It may, however, be carried forward some distance in front of the anal orifice, from which in the breeding season, as in the Voles and Marmots, the prominent testicular mass separates it. The testes in the rutting season form projections in the groins, but (except in the Duplicidentata) do not completely leave the cavity of the abdomen. Prostatic glands and, except in the Duplicidentata, vesiculæ seminales are present in all. The uterus may be double, each division opening by a separate aperture into a common vagina, as in _Leporidæ_, _Sciuridæ_, and _Hydrochœrus_, or completely two-horned, as in most species. The mammæ vary in number and position from the single abdominal pair of the Guinea-Pig to the ten thoracico-abdominal pairs found in some of the Rats. In the _Octodontidæ_ the mammæ are placed high up on the sides of the body.

[Illustration: FIG. 196.—Alimentary canal of Rat (_Mus decumanus_), the greater part of the small intestine being omitted. _o_, Œsophagus; _d_, duodenum; _i_, ileum; _cm_, cæcum; _c_, colon.]

The peculiar odour evolved by many Rodents is due to the secretions of special glands, which may open either into the prepuce, as in _Mus_, _Arvicola_, _Cricetus_, etc., or into the rectum, as in _Arctomys_ and _Aulacodus_ or into the passage common to both, as in the Beaver, or again, into pouches opening near the anus, as in the Hare, Agouti, and Jerboa.

The integument is generally thin, and the panniculus carnosus (the sheet of muscle underlying the skin) rarely much developed. The fur varies exceedingly in character. Thus it may be very fine and soft, as in the Chinchillas and Hares, in others more or less replaced by spines on the upper surface, as in the Spiny-Rats and Porcupines; in several genera, as in _Xerus_, _Acanthomys_, _Platacanthomys_, _Echinothrix_, _Loncheres_, and _Echinomys_, the spines are flattened. In the muscular structures the chief peculiarities are noticeable in the comparatively small size of the temporal muscles, and in the great double masseters (Fig. 194), which are the principal agents in gnawing; the digastrics also are remarkable for their well-defined central tendon, and in many species their anterior bellies are united between the mandibular rami; the cleidomastoid generally arises from the basioccipital, and the pectoralis major is connected with the latissimus dorsi; in the Porcupines and Hares the tendons of the flexor digitorum longus and flexor hallucis longus are connected in the foot, while in the Rats and Squirrels they are separate, and the flexor digitorum longus is generally inserted into the metatarsal of the hallux.[290]

Rodents are tolerably well represented in a fossil condition from the period of the Upper Eocene, while if _Decticadapis_, of the Lower Eocene of Rheims, is rightly referred to it the order dates from the oldest Tertiary. All the fossil forms at present known are, however, essentially true Rodents, and afford no clue as to the relations of the order with other mammals. The remote affinities of the Rodents to the Proboscidea, as well as their more marked resemblances to _Typotherium_, have been already mentioned. Whether there is a real genetic affinity (as Professor Cope suggests) with the Tillodontia cannot be decided with the evidence at present available.

_Suborder_ SIMPLICIDENTATA.

Only one pair of upper incisors, having their enamel confined to their front surfaces. Incisive foramina moderate and distinct; fibula not articulating with the calcaneum. Testes abdominal, and descending periodically only into a temporary sessile scrotum.

_Section_ SCIUROMORPHA.

Zygomatic arch slender, chiefly formed by the jugal, which is not supported by a long maxillary process extending backwards beneath it; postorbital processes of frontal present or absent; infraorbital opening small (except in _Anomalurus_); mandible with the angular part arising from the inferior surface of the bony socket of the lower incisor; clavicles well developed; fibula distinct.

_Family_ ANOMALURIDÆ.

Arboreal forms, having their limbs connected by a cutaneous expansion supported by a cartilaginous process arising from the olecranon; tail long and hairy, with large imbricated scales on its inferior surface near the root; sixteen pairs of ribs; no postorbital processes on the frontals; _p_ ¹⁄₁; molars not tuberculate, with transverse enamel-folds. Confined to the Ethiopian region.

[Illustration: FIG. 197.—_Anomalurus fulgens._ From Alston, _Proc. Zool. Soc._ 1875.]

_Anomalurus_,[291] with several species from West and Central Africa, alone represents the family. The peculiar caudal scales, which evidently assist the animal in climbing, and the position of the cartilaginous support of the parachute, are well shown in Fig. 197. All the species but two are from Western Africa; _A. orientalis_ occurs near Zanzibar, and _A. pusillus_ is from the equatorial regions of that continent. According to Mr. O. Thomas,[292] the latter “little animal is most nearly allied to the West-African _A. beecrofti_, but differs from that species in its duller and less yellow upper side, in the entire absence of rufous on its neck and belly, and, as from all the other described species, in its diminutive size.”

_Family_ SCIURIDÆ.

Arboreal or terrestrial forms, with cylindrical hairy tails, without scales, and with twelve or thirteen pairs of ribs. Skull (Figs. 198, 199) with distinct postorbital processes; infraorbital opening small; palate broad; _p_ ²⁄₁; first upper premolar very small or deciduous; molars rooted, tubercular.

Subfamily =Sciurinæ=.—Incisors compressed; form slender; tail long and hairy. Cosmopolitan (excluding Australian region).

[Illustration: FIG. 198.—Lateral view of skull of American Marmot (_Arctomys monax_).]

This subfamily includes the true Squirrels, of which seven existing genera are usually recognised.

_Sciurus._[293]—Tail long and bushy; ears generally well developed, pointed, often tufted; feet adapted for climbing, the anterior having four digits and a rudimentary pollex, and the posterior with five digits, all of which have long, curved, and sharp claws. Mammæ, from four to six. Skull (Fig. 199) lightly built, with long postorbital processes. Penultimate upper premolar, when present, minute.

[Illustration: FIG. 199.—Palatal Aspect of cranium of Squirrel (_Sciurus bicolor_). Natural size.]

True Squirrels are found in most of the temperate and tropical regions of the world, exclusive of Madagascar and the Australian region. They are, however, most abundant in the Malayan part of the Oriental region, and attain their largest size and most brilliant coloration in the tropics. Their size is very variable, so that whereas _S. soricinus_, of Borneo, is no larger than a Mouse, _S. bicolor_, of the Malayan region, is nearly as large as a Cat. The common English Squirrel (_S. vulgaris_) is found over the whole of the Palæarctic region, reaching in one direction from Ireland to Japan, and in the other from the north of Italy to Lapland; its remains occur in the Norfolk “Forest-bed.” In the Malayan region “nearly all the numerous species are brilliantly marked, and many are ornamented with variously coloured longitudinal stripes along their bodies. One of the commonest and best known of the striped species is the little Indian Palm-Squirrel (_S. palmarum_), which in large numbers runs about every Indian village. Another Oriental species (_S. caniceps_) presents almost the only known instance among mammals of the temporary assumption during the breeding season of a distinctly ornamental coat, corresponding to the breeding-plumage of birds. For the greater part of the year the animal is of a uniform gray colour; but about December its back becomes a brilliant orange-yellow, which lasts until about March, when it is again replaced by gray. The Squirrel shown in Fig. 200 is a native of Burma and Tenasserim, and is closely allied to _S. caniceps_, but goes through no seasonal change of colour.

[Illustration: FIG. 200.—Burmese Squirrel (_Sciurus pygerythrus_). After Anderson.]

“The number of species in the genus is about 75, of which 3 belong to the Palæarctic, 15 to the Ethiopian, about 40 to the Oriental, and 16 to the combined Nearctic and Neotropical regions” (Thomas).

Fossil species referred to _Sciurus_ are found in the European Tertiaries down to the Phosphorites of Central France, while others occur in the White River Miocene of the United States.

_Rhithrosciurus._[294]—A very striking Squirrel, confined to Borneo, and as yet only known from three or four examples, has been separated generically under this name. The general shape of its skull is very different from that of other Squirrels; but its most peculiar characteristic is the presence of from seven to ten minute parallel vertical grooves running down the front face of its incisors; no other Squirrel having really grooved incisors, and no other member of the whole order incisive grooves resembling these. Its premolars number ¹⁄₁, and its molars are simpler and less ridged than in the other genera. This Squirrel (_R. macrotis_) is far larger than the English, with an enormously long bushy tail, long tufted ears, and black and white bands down its sides.

_Xerus._[295]—Fur coarse and spiny. Claws long and comparatively straight. Ear-conchs minute or absent. Skull with the postorbital processes short and directed backwards, the bony palate prolonged considerably behind the tooth-row, and the external ridge on the front face of the anterior zygomatic root more developed, and continued much farther upwards than in _Sciurus_. Premolars ²⁄₁; molars as in _Sciurus_. Mammæ two. This genus contains four well-marked species, known as Spiny Squirrels, all natives of Africa. They are terrestrial in their habits, living in burrows which they dig for themselves. _X. getulus_, a striped species of North Africa, has much the size and appearance of the Indian Palm-Squirrel; all the others are a little larger than the English Squirrel.

_Tamias._[296]—All the members of this genus are characterised by the possession of internal cheek-pouches, and by their style of coloration; being ornamented on the back with alternate light and dark bands. Their skulls are slenderer and lighter than those of the true Squirrels, from which they differ in several unimportant details. There is only one functional premolar—the small anterior one usually found in _Sciurus_ being either absent altogether or quite small and functionless. There are some four well-defined species, all found in North America, one (_T. asiaticus_) extending also through Siberia into Eastern Europe.[297] They are generally known as Ground-Squirrels, but in America, where they are among the commonest and best known of the indigenous Rodents, as “Chipmunks.” The members of this genus seem to lead into the genus _Spermophilus_, so that the division of the _Sciuridæ_ into two subfamilies, although convenient for classification, is rather artificial.

Remains of _Tamias_, probably belonging to existing species, occur in the Pleistocene deposits of Europe and Nebraska.

_Pteromys_[298] and _Sciuropterus_.[299]—The Flying Squirrels, although incapable of true flight, can yet float through the air for considerable distances by the aid of an extension of skin connecting their fore and hind limbs, and forming a sort of parachute. This parachute is merely a lateral extension of the ordinary skin of the body, which passes outwards between the limbs and terminates at the wrists and ankles. In addition to the lateral membrane there is a narrow and inconspicuous one passing from the cheek along the front of the shoulder to the front of the wrist, and another—at least in the larger species—stretching across behind the body from ankle to ankle and involving the base of the tail. The Flying Squirrels are divided into three genera. Of those with a normal dentition _Pteromys_ contains the larger and _Sciuropterus_ the smaller species. The two differ in certain details of dentition, as well as in the greater development in the former of the expanded membranes, especially of the “interfemoral” or posterior membrane, which in the latter is almost wholly absent. In _Pteromys_ the tail is cylindrical and comparatively thin, while in _Sciuropterus_ it is broad, flat, and laterally expanded, and evidently compensates for the absence of the interfemoral membrane by acting as a supplementary parachute. In appearance Flying Squirrels resemble the other forms, although they are even more beautifully coloured. Their habits, food, etc., are also very similar to those of the true Squirrels, except that they are more decidedly nocturnal, and are therefore less often seen by the traveller; their peculiar shrill cry is, however, well known to all who have camped out in the regions which they inhabit. Their mode of flight is precisely similar to that of the Flying Phalangers of Australia. Of each of the two genera there are about thirteen or fourteen species, all natives of the Oriental region, except that one of _Sciuropterus_ is found in North America, and another in Siberia and Eastern Europe.

_Eupetaurus._[300]—Externally as in _Pteromys_, except that the claws are less sharp. Skull with a more produced muzzle than in the latter, more distinct supraorbital notches, longer anterior palatal foramina, and a shorter bony palate. Cheek-teeth differing from those of all other _Sciuridæ_ in their hypsodont character. One large species (_E. cinereus_), from Gilgit and adjacent districts on the extreme north-west of Kashmir territory. This fine Flying Squirrel is chiefly known by one entire specimen and some imperfect skins.

_Extinct Genera._—The genera _Pseudosciurus_ and _Sciuroides_, from the Upper Eocene of Europe, have the molar teeth more elongated than in _Sciurus_. _Gymnoptychus_ with _p_ ¹⁄₁, from the North American Miocene, approximates in the structure of its molars to _Tamias_. _Meniscomys_ (_p_ ²⁄₁), from the latter deposits, together with _Sciurodon_ of the French Phosphorites, are regarded as Squirrels showing signs of affinity with the _Haplodontidæ_.

Subfamily =Arctomyinæ=.—Incisors not compressed; typically the form stout, and the tail comparatively short. This subfamily comprises burrowing forms which may be collectively known as Marmots; as already mentioned, they are so intimately connected with the preceding subfamily that the division into two groups is purely a matter of convenience. They are confined to the Palæarctic and Nearctic regions.

_Arctomys._[301]—External form stout and heavy, ears short, tail short and hairy, cheek-pouches rudimentary or absent. Fore feet with four well-developed digits, and a rudimentary pollex provided with a flat nail. Skull (Fig. 198) large and heavy, with the postorbital process stout, and at right angles to the axis. Incisors broad and powerful. First upper premolar nearly as large as the second. Molar series nearly parallel, scarcely converging behind at all.

The various species of true Marmot, which exceed a dozen in number, are all much alike in general appearance, ranging in size from about 15 to 25 inches in length, with tails from 3 to 12 inches long.

The Alpine Marmot (Fig. 201) is peculiar to Europe, being found in the Alps, Pyrenees, and Carpathians; its remains occur in European Pleistocene deposits. _A. bobac_ occurs in Eastern Europe and Siberia. Several species (_e.g._ _A. monax_, Fig. 198) are found in the Nearctic region, and many in Kashmir and Central Asia. The long-tailed Red Marmot (_A. caudatus_) is a fine Himalayan species, which may be seen on the mountain passes to the north of the valley of Kashmir, as soon as the snow begins to disappear, sitting at the entrance to its burrow, which is generally beneath a rhubarb plant.

[Illustration: FIG. 201.—Alpine Marmot (_Arctomys marmotta_). After Brehm.]

The following account of the habits of the Alpine Marmot is given by Professor Blasius: “Marmots live high up in the snowy regions of the mountains, generally preferring exposed cliffs, whence they may have a clear view of any approaching danger, for which, while quietly basking in the sun or actively running about in search of food, a constant watch is kept. When one of them raises the cry of warning, the loud piercing whistle so well known to travellers in the Alps, they all instantly take to flight and hide themselves in holes and crannies among the rocks, often not reappearing at the entrance of their hiding-places until several hours have elapsed, and then frequently standing motionless on the look-out for a still longer period. Their food consists of the roots and leaves of various Alpine plants, which, like squirrels, they lift to their mouths with their fore paws. For their winter quarters they make a large round burrow, with but one entrance, and ending in a sleeping-place thickly lined with hay. Here often from ten to fifteen Marmots pass the winter, all lying closely packed together fast asleep until the spring.”

_Cynomys._[302]—Size and form intermediate between _Arctomys_ and _Spermophilus_. Ears and tail short. Cheek-pouches shallow. Fore feet with five claws, that on the pollex as large as that on the fifth toe. Skull (Fig. 202) heavily built, with the postorbital processes directed outwards. Dentition (as shown in Fig. 202) remarkably heavy, the molar teeth differing from those of _Arctomys_ and _Spermophilus_ by having three instead of two transverse grooves on their crowns. First premolar nearly as large as the second. Molar series strongly convergent behind.

Two species of Prairie Marmots, or, as they are often called, “Prairie-Dogs,” are found in North America. They live together in large communities, inhabiting burrows excavated at short distances apart, and feeding on the buffalo-grass which covers the plains. The small burrowing owl (_Athene cunicularia_) and the rattlesnake are often found inhabiting their burrows; the former probably availing itself of the convenience of a ready-made habitation, the latter coming there to feed on the young Marmots.

[Illustration: FIG. 202.—Palatal aspect of the cranium of the Prairie Marmot (_Cynomys ludovicianus_).]

_Spermophilus._[303]—Size much smaller than in either of the preceding genera; form more slender and squirrel-like. Tail very variable, from 1 to 8 or 9 inches in length. Cheek-pouches always present. Fore feet with four well-developed toes and a rudimentary pollex, of which the claw may be either present or absent. Skull more lightly built than in the other preceding genera, with the postorbital processes slender and directed backwards. Molar series nearly parallel, as in _Arctomys_, but all these teeth much smaller and lighter; first premolar simply rounded, never more than about one-third of the size of the second.

The Pouched Marmots, or Sousliks, have nearly the same distribution as _Tamias_, and are represented by a considerable number of species. They present a far greater range of variation than is found among the true Marmots, some of them, such as the European species, being scarcely as large as a common squirrel, almost entirely without external ears, and with the tail reduced to a mere stump, barely an inch long, while others are more than three times this size, with large and often tufted ears, and long bushy squirrel-like tails. Professor Blasius gives the following details of the habits of the common European Souslik (_S. citillus_): “It lives in dry treeless plains, especially on a sandy or clayey soil, and is never found either in forests or on swampy ground. It forms burrows, often 6 or 8 feet deep, in which food is stored up and the winter sleep takes place. Each burrow has but one entrance, which is closed up when winter approaches,—a second hole, however, being previously formed from the sleeping-place to just below the surface of the ground. The second hole is opened the next year, and used as the ordinary entrance, so that the number of closed-up holes round a burrow gives an indication of the length of time that it has been occupied. Sousliks ordinarily feed on roots, seeds, berries, etc., but occasionally also on animal food, preying readily on eggs, small birds, and mice, the remains of these latter being often found in their burrows. They bring forth in the spring from four to eight young ones, which, if taken early, may be easily tamed. They are often eaten by the peasants, the inhabitants of the Russian steppes considering their flesh an especial delicacy.”

Remains of _Spermophilus_ are not uncommon in European Tertiary deposits, some belonging to living and others to extinct species.

_Extinct Genera._—_Plesispermophilus_, from the Upper Eocene Phosphorites of Central France, appears to be closely allied to the Sousliks. _Plesiarctomys_ (_Sciuravus_ or _Paramys_), which is common to the Middle Tertiaries of Europe and North America, appears to be a generalised form, showing some resemblance both to _Arctomys_ and _Sciurus_, but with tritubercular upper molars and no postorbital processes to the skull; in the latter respect agreeing with the next family. In the size of the preorbital vacuity the skull resembles the Hystricomorpha.

_Family_ HAPLODONTIDÆ.

Distinguished from the _Sciuridæ_ by the absence of postorbital processes to the frontals, the depressed skull, and the rootless cheek-teeth. Premolars ²⁄₁; the penultimate upper one small.

_Haplodon._[304]—_H. rufus_ and _H. major_, of North America, west of the Rocky Mountains, are the only representatives of the family; their habits are similar to those of _Cynomys_.

_Family_ CASTORIDÆ.

Skull massive, without postorbital processes, the angle of the mandible rounded, and the cheek-teeth rootless, with re-entering enamel-folds. Premolars ¹⁄₁. Habits natatorial.

_Castor._[305]—The upper molars are subequal, each with one internal and two external enamel-folds; the stomach has a large glandular mass situated to the right of the œsophageal orifice; the anal and urethro-genital orifices open within a common cloaca; the tail is broad, horizontally flattened, and naked; and the hind feet are webbed. One or two species, Palæarctic and Nearctic.

Zoologists are not yet of accord as to whether the European and American Beavers should be regarded as distinct species or as local races; the general concensus of opinion being in favour of the latter view.

The European Beaver (_C. fiber_) was at one time an inhabitant of the British Isles, having been found, according to Pennant, in certain Welsh rivers so late as the twelfth century, while subfossil remains of it occur in the peat-beds of many parts of the country. In Scandinavia Beavers are still found in the neighbourhood of Arendal. Isolated pairs are occasionally met with on the banks of the Rhone, Weser, and Elbe; and a considerable number are kept in a park belonging to the Emperor of Austria, on the banks of the Danube. They also occur sparingly in Russia and Poland, in the streams of the Ural Mountains, and in those which flow into the Caspian. They live in burrows on the banks of rivers, like the Water-Rat, and show little of the architectural instinct so conspicuous in the American form, but this may be owing to unfavourable external conditions rather than to want of the faculty; for there is a well-authenticated instance of a colony of Beavers, on a small stream near Magdeburg, whose habitations and dam were exactly similar to those found in America.

The American Beaver (_C. canadensis_) extends over that part of the American continent included between the Arctic circle and the tropic of Cancer; owing, however, to the gradual spread of population over part of this area, and still more to the enormous quantity of skins that, towards the end of last and the beginning of the present century, were exported to Europe, numbering about 200,000 annually, this species is in imminent danger of extirpation. It is distinguished from the European Beaver by the shorter and somewhat wider nasals.

Remains of extinct species of _Castor_ occur in the Pliocene of Europe, and in the North American Miocene; the one from the last-mentioned deposits being of small size, and separated by some writers as _Eucastor_.

_Extinct Genera._—A very large Beaver known as _Trogontherium_ (_Diobroticus_), and distinguished by the nature of the enamel-folds of the molars, occurs in the Upper Pliocene and Pleistocene of Europe. _Chalicomys_ (_Steneofiber_) is a considerably smaller form from the Miocene of Europe and the United States, distinguished from all existing Rodents by the presence of an entepicondylar foramen in the humerus. _Palæocastor_, of the North American Miocene, is allied.

_Section_ MYOMORPHA.

[Illustration: FIG. 203.—Side view of skull of _Fiber zibethicus_, natural size.]

Skull (Fig. 203), with slender zygomatic arch, in which the jugal seldom extends far forwards, being usually supported by the long zygomatic process of the maxilla; no postorbital process; infraorbital vacuity variable; angle of mandible, except in the _Bathyerginæ_, rising from the inferior surface of the incisive alveolus. Clavicles well developed, except in _Lophiomys_. Tibia and fibula united.

_Family_ MYOXIDÆ.

Small arboreal forms, with long hairy tails, large eyes and ears, and short fore limbs. No cæcum in the intestine. Skull with narrow frontals, a high and narrow infraorbital vacuity of moderate size, and a long and slender coronoid process to the mandible. Premolars ¹⁄₁; molars rooted, with transverse enamel-folds.

The Dormice form a natural family allied to the Squirrels in form and habits, and confined to the Palæarctic and Ethiopian regions. The absence of the cæcum distinguishes them from all other members of the order. They are usually divided into the following five genera, but some of these are of very doubtful value, and it might be preferable to retain _Muscardinus_ and include all the others in _Myoxus_.[306]

_Myoxus._[307]—Represented by the European _M. glis_, and characterised by the bushy distichous tail, simple stomach, and the large size and complex enamel-folds of the molars, which have flat crowns.

_Eliomys._[308]—Tail tufted and distichous; stomach simple; and the molars small, with concave crowns and indistinct enamel-folds. Some seven species, Ethiopian and Palæarctic.

_Graphiurus._[309]—Tail short, cylindrical, and tufted at the end; molars very small, with the enamel-folds almost absent. Some three Ethiopian species.

_Claviglis._[310]—Represented by one West African species, said to be distinguished from all other forms by the shorter tail, which is more distinctly pencilled. The right to generic distinction is, however, very problematical.

_Muscardinus._[311]—Includes the Common Dormouse (_M. avellanarius_) of Europe, distinguished by the cylindrical bushy tail, and thickened glandular walls of the cardiac extremity of the œsophagus; the molars have flat crowns, with complex enamel folds.

_Fossil Dormice._—Using the generic term _Myoxus_ in a more extended sense than the above, it has existed in Europe from the date of the Upper Eocene. A species nearly as large as a Guinea-Pig, with very complex molars, is common in the Pleistocene of Malta.

_Family_ LOPHIOMYIDÆ.

[Illustration: FIG. 204.—_Lophiomys imhausi_. From Milne-Edwards.]

The genus _Lophiomys_,[312] represented only by _L. imhausi_ (Fig. 204) of North-East Africa, differs from the typical _Muridæ_ in having the temporal fossæ roofed over by a thin plate of bone, rudimentary clavicles, and an opposable hallux. On these grounds it has been made the type of a family, but since all the features are Murine—the dentition being that of a typical Cricetine—it appears doubtful whether that distinction is justifiable. The hair forms a crest along on the back, and is of a peculiar structure. The habits of this Rodent are arboreal.

_Family_ MURIDÆ.

Skull (Fig. 203) with contracted frontals; a short and slender jugal, generally reduced to a splint between the zygomatic processes of the maxilla and squamosal; the lower root of the former process more or less flattened into a perpendicular plate; typically, the infraorbital vacuity tall, and wide above and narrow below. Lower incisors compressed; no premolars;[313] molars rooted, or rootless, tuberculate, or with angular enamel-folds. Pollex rudimental; tail generally nearly naked and scaly. Habits various, but mostly terrestrial.

This large and cosmopolitan family, which includes more than a third of the existing Rodents, is represented by about forty genera.

Subfamily =Hydromyinæ=.—Molars ²⁄₂ in number, rooted, and divided into transverse lobes. Represented by two Australasian genera.

_Hydromys._[314]—External form modified for an aquatic life. Tip of muzzle extensively haired, so that the nostrils can be closed. Skull with the infraorbital vacuity crescentic, scarcely narrowed below, and its external wall without the perpendicular zygomatic plate characteristic of most of the family; incisive foramina very small.

Two species, with habits like those of the Water Voles, are known from Australia, Tasmania, and New Guinea. In the typical _H. chrysogaster_ the colour of the back is black, with an admixture of golden-coloured hairs; the belly being of a dark golden hue.[315]

_Xeromys._[316]—External form Murine. Tip of muzzle as in _Mus_, not as in _Hydromys_. Toes unwebbed. Tail scaly, very finely haired. Skull as in _Mus_, with the exception of the rounding of the supraorbital edges. Teeth as in _Hydromys_.

Represented by _X. myoides_, of Queensland; a species about twice the size of the Common Mouse. This genus serves to connect _Hydromys_ with the other Murines, although it is difficult to say to which group it comes nearest.

Subfamily =Platacanthomyinæ=.—Molars rooted, with transverse laminæ. Flattened spines mingled with the hair; tail thickly haired. Represented by one genus.

_Platacanthomys._[317]—The one representative of this genus is _P. lasiurus_, found in the clefts of rocks and hollow trees in Southern India at elevations of about 3000 feet. This elegant little animal closely resembles a Dormouse; the tail and body having a length of 6 inches.

Subfamily =Gerbillinæ=.—Incisors narrow; molars with transverse laminæ (Fig. 205). Auditory bullæ very large in most cases. Hind limbs elongated. Tail usually long and hairy. Ranges over the Palæarctic, Oriental, and Ethiopian regions.

_Gerbillus._[318]—Upper incisors grooved; first molar with three laminæ, second with two, and third with one. There are some sixty species, with a range coextensive with that of the family. The Gerbils, with their large and bright eyes and long tufted tails, are very graceful creatures, inhabiting sandy plains, where they form extensive burrows. Remains of existing species are found in cavern-deposits in Madras (Fig. 205).

[Illustration: FIG. 205.—The left ramus of the mandible of _Gerbillus indicus_, with an enlarged view of the molars, from a cavern deposit in Madras. (From the _Palæontologia Indica_.)]

_Pachyuromys._[319]—The African genus _Pachyuromys_ is distinguished by the very large size of the auditory bulla, as well as by the short and fleshy tail, which is club-shaped. The incisors are narrow and faintly grooved.

_Mystromys_,[320] _Otomys_,[321] and _Dasymys_.[322]—These genera, also from South Africa, differ from _Gerbillus_ in the form of the molars, and are represented by a few species.

_Malacomys._[323]—The one known species of this genus is from the Gaboon, and is in some respect intermediate between the true Gerbils and the Rats. Thus the dentition and feet are those of the former, but the long scaly tail resembles that of the latter.

Subfamily =Phlœomyinæ=.[324]—This subfamily is represented only by _Phlœomys_[325] _cumingi_, of the Philippine Islands, in which the incisors are very broad, the molars are divided into transverse laminæ, and the claws are large. The muzzle is blunt; the ears are hairy externally; the tail is moderate, and thickly haired; and the auditory bullæ are very small. The first upper molar has three, and the others two laminæ.

Subfamily =Dendromyinæ=.—Incisors convex in front; molars ³⁄₃, rooted and tuberculated. Ears hairy; claws long. Confined to the Ethiopian region.

_Dendromys._[326]—A small Rodent, with the habits of a Dormouse, characterised by its grooved incisors, slender form, and long, scaly tail, which is sparsely haired. Two other Murines described as _Steatomys_[327] and _Lophuromys_[328] are referred to this subfamily. The first is of plump form, with a rather short and thickly haired tail, and grooved incisors. The latter resembles _Steatomys_ in form, but has fine flattened bristles instead of fur, and plain incisors.

Subfamily =Cricetinæ=.—Molars ²⁄₃, tuberculate and rooted, with the tubercles of the upper ones arranged in two longitudinal rows (Fig. 206, _B_). This subfamily has an almost cosmopolitan distribution, and appears to include the most generalised members of the family, from which the more specialised _Murinæ_ have been evolved.

_Cricetus._[329]—According to the arrangement proposed by Mr. O. Thomas[330] this genus is taken to include both the Hamsters of the Old World (_Cricetus_ proper) and the white-footed or Vesper Mice (_Hesperomys_) of the New. Cheek-pouches are frequently present, and may be very large. The first molar (Fig. 206, _B_) generally has six tubercles. The tail may be very short.

[Illustration: FIG. 206.—Left upper molars of _Mus_ (_A_) and _Cricetus_ (_B_).]

This large and unwieldy genus may be divided into a number of groups or subgenera. The typical group includes the Hamsters of the Old World, characterised by the large size of their cheek-pouches, the walls of which are connected with muscles arising from the lumbar vertebræ. The tail is remarkable for its shortness. The best-known species is _C. frumentarius_, inhabiting Europe and Northern Asia. The American forms, which range over the whole of that continent, comprise a number of subgenera, of which the following are the most important. _Rhipidomys_, including Dormouse-like forms with long tails and a dentition like that of the typical group; _Oryzomys_, represented by Murine species; _Calomys_, with short tail and Hamster-like body; _Vesperimus_, with only five tubercles on the first molar; _Onychomys_, in which the tail is extremely short and Hamster-like, and the form is Arvicoline; _Scapteromys_, of Murine form with a long and hairy tail; _Phyllotis_, with a shorter tail; _Habrothrix_, an Arvicoline group, with a short and thinly haired tail; and _Oxymycterus_, distinguished from the preceding by having a nail instead of a claw on the pollex. With regard to the distribution of these forms Mr. Thomas[331] remarks that in South America as we proceed southwards there is a general tendency “to a disappearance of the tropical and northern Mouse- and Dormouse-like subgenera _Rhipidomys_, _Vesperimus_, and _Oryzomys_, with the appearance and increase of the Vole- and Hamster-like _Habrothrix_ and _Calomys_—a change that is curiously paralleled in the Old World by the gradual supercession of _Mus_ and _Myoxus_ in favour of _Arvicola_ and _Cricetus_ as we go northwards from tropical to temperate and arctic regions.” One species has spines in the fur.

Remains of _Cricetus_ are abundant in the Pleistocene cavern-deposits of Brazil, where a number of the forms are referable to existing species; the genus is also represented in the Miocene of North America and Europe, the species from the former area having been described as _Eomys_, and those from the latter as _Cricetodon_.

_Holochilus_[332] (_Nectomys_).—The Rats of this genus are allied to the American forms of _Cricetus_, but have the third upper molars proportionately larger and the skull more stoutly built. This genus is confined to Brazil, and contains about six species, some of which are the largest indigenous Rats of America. Two species are aquatic in their habits, and have short webs between the toes of their hind feet.

_Sigmodon_[333] differs from _Cricetus_ in the pattern of the molar teeth. It contains one species only, the Rice-Rat, _S. hispidus_, ranging from the United States to Ecuador.

_Rhithrodon_,[334] and _Ochetodon_.[335]—These are more or less like _Cricetus_, but with grooved upper incisors. The first, is a South-American genus, and contains five Rat-like species, one from Venezuela, another from Peru, and the other three from Patagonia. The second consists of three North American mice, of about the size and proportions of the English Wood-Mouse (_Mus sylvaticus_).

_Neotoma._[336]—A peculiar North American genus, in which the teeth simulate the prismatic appearance of those of the _Arvicolinæ_. There are four species known as Wood-Rats, all of about the size of _Mus decumanus_; one of them (_N. cinerea_) having a tail almost as bushy as a Squirrel’s while the other three have ordinary scaly Rat-like tails.

Fossil remains of _Neotoma_ from cavern-deposits in Pennsylvania are not improbably referable to the existing Florida Rat (_N. floridana_). _Paciculus_, from the Miocene of the United States, is regarded as an allied extinct genus with enamel-folds to the molars.

_Hypogeomys._[337]—This and the following genera are confined to Madagascar, where they are the sole representatives of the Rodentia. _Hypogeomys_ is a very peculiar form of large size, with long ears, feet, and tail. There is only one species, _H. antimena_, a fawn-coloured Rat about 9 inches long.

_Nesomys._[338]—Contains two species of long-haired Rats, more or less rufous in colour, about the size of the Brown Rat.

_Brachytarsomys._[339]—Represented only by _B. albicauda_, a pretty velvety-haired fawn-coloured Rat, with short feet and a long tail.

_Hallomys._[340]—The only species (_H. audeberti_) is very like a _Nesomys_, but has much longer hind feet.

_Eliurus._[341]—Represented by one small Dormouse-like species, characterised by its nearly naked and short ears, and long tail, of which the proximal third is scaly, and the remainder covered with long hair. The pollex is rudimental, but the hallux well developed.

Subfamily =Arvicolinæ=.—Molars usually imperfectly rooted or rootless, and composed of two longitudinal rows of triangular prisms placed alternately (Fig. 207). Tail moderate or short. Common to the Palæarctic and Nearctic regions.

[Illustration: FIG. 207.—Upper (_A_) and lower (_B_) molars of the Water-Vole (_Arvicola amphibius_).]

The Voles, as the members of this group are commonly termed, are so closely connected with the Cricetines that they may be regarded merely as a branch of that subfamily which has attained a peculiarly specialised type of molar dentition. The Voles are externally distinguished, as a rule, from true Rats and Mice by their more clumsy and heavy build and less graceful movements; by the small size of their eyes, the bluntness of the muzzle, the small ears, and the shorter limbs and tail.

_Phenacomys._[342]—A North American genus distinguished by its rooted molars, and thus connecting the typical forms with Cricetines like _Neotoma_. Several species have been described by Dr. C. H. Merriam.

_Arvicola._[343]—The type genus _Arvicola_ has rootless molars, and naked soles to the feet. It includes over forty species inhabiting Europe, North America, and Asia, a few species entering into the northern limits of the Oriental region in India. Three species of the genus are found in the British Isles, of which the following account is given by Mr. O. Thomas:—

The common Water-Vole (_A. amphibius_) is as large as the Brown Rat. Its fur is long, soft, and thick, of a uniform grizzled brown all over, except when, as is not uncommon, it is wholly black. The tail is about half the length of its head and body, and the hind feet are unusually long and powerful, although not webbed, and have five rounded pads on their lower surfaces. Its molar teeth (see Fig. 207) present the following number of prismatic spaces:—in the upper jaw the first, or anterior, has 5, the second 4, and the third 4, of which the last is very irregular in shape, and is sometimes itself divided into two, making 5 in all; in the lower jaw the first has 7 spaces, of which the 3 anterior are generally not fully separated from one another, the second has 5, and the third 3. These numbers for the different teeth are taken as the characters of the subgenus _Paludicola_ of Dr. Blasius, by whom this method of subdividing the genus was first introduced. The Water-Vole is one of the commonest English mammals, and is perhaps the most often actually seen of all, owing to its diurnal habits. It frequents rivers and streams, burrowing deeply into their banks, and in this way often causing considerable damage. Its food consists almost wholly of water-weeds, rushes, and other vegetable substances, but, like so many other Rodents, it will also occasionally eat animal food, in the shape of insects, mice, or young birds. The female during the warm season of the year has three or four litters, each of from two to seven young. The range of the Water-Vole extends over the whole of Europe and North Asia, from England to China, but it is not found in Ireland. The common Field-Vole, or short-tailed Field-Mouse (_A. agrestis_), representing the subgenus _Agricola_, is about the size of a House-Mouse, but with a short stumpy body, and a tail only about one third the length of the head and body combined. Its hind feet have six pads on their inferior surfaces. The colour is dull grizzled brown above, and grayish-white below. Its molar teeth have respectively 5, 5, and 6 prismatic spaces above, and 9, 5, and 3 below. The Field-Vole is one of the commonest of our smaller mammals, and frequents fields, woods, and gardens in enormous numbers, often doing very considerable damage in the latter, owing to its fondness for garden produce of all kinds. It is spread over the whole of Great Britain from the Hebrides southwards. Abroad its range extends from Finland to North Italy and from France and Spain to Russia. The Bank-Vole (_A. glareolus_) resembles in size and general appearance the common Field-Vole, but may be distinguished by its more or less rusty or rufous-coloured back, its larger ears, and the relatively longer tail, which attains to about half the length of the head and body. Its molar teeth present characters so different from those of all other Voles as to have caused it to be regarded as belonging to an entirely distinct genus, for which the name of _Evotomys_ has been used. Their chief distinction lies in the fact that, unlike those of all other Voles, their pulp-cavities close up in adult life, and they form distinct roots, more resembling those of the ordinary Rats and Mice. The enamel-spaces of these teeth number respectively 5, 4, and 5 above, and 7, 3, and 3 below. The habits of this species are in every way similar to those of the Field-Vole. Its range in Great Britain extends northwards to Morayshire, beyond which it has not yet been observed. It is also found all along the north temperate zone from France to China, and is replaced in North America by a closely allied animal known as _A. gapperi_. It is probable, however, that both _A. gapperi_ and _A. glareolus_ are only southern climatic offshoots of a still more northern species, the _A. rutilus_ of Northern Europe, Siberia, and Arctic America.

Fossil remains of _Arvicola_ are common in European Pleistocene deposits, and they have also been obtained from the Upper Pliocene of the Norwich Crag.

_Synaptomys._[344]—Represented by one North American species, having grooved upper incisors, skull and molars like those of _Myodes_, with the external characters of _Arvicola_.

_Myodes._[345]—Distinguished from _Arvicola_ by the more clumsy build, convex obtuse head, extremely short and Rabbit-like tail, short ears, small feet, the soles of which are furred, elongated claws, and thick fur, as well as by the breadth and massiveness of the skull, in which the zygomatic arch has a laminar expansion and the palate a peculiar contour; while the root of the lower incisor does not extend behind the last molar, the upper incisors are bevelled, and not grooved, and the molars have a characteristic pattern, which cannot be well explained without a figure.

[Illustration: FIG. 208.—The Lemming (_Myodes lemmus_).]

The Lemmings, as the members of the genus are commonly called, are represented by the Norwegian Lemming (_M. lemmus_, Fig. 208), and the North American _M. obensis_. Different individuals of the Norwegian Lemming vary considerably both in size and colour, but its usual length is about 5 inches, and its soft fur yellowish brown, marked with spots of dark brown and black. It has a short, rounded head, obtuse muzzle, small bead-like eyes, and short rounded ears, nearly concealed by the fur. The tail is very short. The feet are small, each with five claws, those of the fore feet strongest, and fitted for scratching and digging. The usual dwelling place of the Lemmings is in the highlands or fells of the great central mountain chain of Norway and Sweden, from the southern branches of the Langfjeldene in Christiansand-stift to the North Cape and the Varangerfjord. South of the Arctic circle they are, under ordinary circumstances, exclusively confined to the plateaus covered with dwarf birch and juniper above the conifer region, though in Tromsö-amt and in Finmarken they occur in all suitable localities down to the level of the sea. The nest is formed under a tussock of grass or a stone, constructed of short dry straws, and usually lined with hair. The number of young in each nest is generally five, sometimes only three, but occasionally seven or eight, and at least two broods are produced annually. Their food is entirely vegetable, especially grass-roots and stalks, shoots of the dwarf birch, reindeer-lichens, and mosses, in search of which they form, in winter, long galleries through the turf or under the snow. They are restless, courageous, and pugnacious little animals. When suddenly disturbed, instead of trying to escape they will sit upright, with their back against a stone or other coign of vantage, hissing and showing fight in a very determined manner (Fig. 208).

The circumstance which has given more popular interest to the Lemming than to a host of other species of the same order of animals is that certain districts of the cultivated lands of Norway and Sweden, where in ordinary circumstances they are quite unknown, are occasionally and at very uncertain intervals, varying from five to twenty or more years, literally overrun by an army of these little creatures, which steadily and slowly advance, always in the same direction, and regardless of all obstacles, swimming across streams and even lakes of several miles in breadth, and committing considerable devastation on their line of march by the quantity of food they consume. In their turn they are pursued and harassed by crowds of beasts and birds of prey, as bears, wolves, foxes, dogs, wild cats, stoats, weasels, eagles, hawks, and owls, and never spared by man; even the domestic animals not usually predaceous, as cattle, goats, and reindeer, are said to join in the destruction, stamping them to the ground with their feet, and even eating their bodies. Numbers also die from diseases apparently produced from overcrowding. None ever return by the course by which they came, and the onward march of the survivors never ceases until they reach the sea, into which they plunge, and swimming onwards in the same direction as before perish in the waves. These extraordinary and sudden appearances of vast bodies of Lemmings, and their singular habit of persistently pursuing the same onward course of migration, have given rise to various speculations, from the ancient belief of the Norwegian peasants, shared in by Olaus Magnus, that they fall down from the clouds, to the almost equally untenable hypothesis, ingeniously maintained by the late Mr. W. D. Crotch, that they are acting in these migrations in obedience to an instinct inherited from vastly ancient times, and are still seeking the congenial home in a supposed submerged Atlantis, to which their ancestors of the Miocene period were wont to resort when driven from their ordinary dwelling-places by crowding or scarcity of food. The principal really ascertained facts regarding these migrations seem to be as follows. When any combination of circumstances has occasioned an increase in the numbers of the Lemmings in their ordinary dwelling-places, impelled by the restless or migratory instinct possessed in a less developed degree by so many of their congeners, a movement takes place at the edge of the elevated plateau, and a migration towards the lower-lying land begins. The whole body moves forward slowly, always advancing in the same general direction in which they originally started, but following more or less the course of the great valleys. They only travel by night; and, staying in congenial places for considerable periods, with unaccustomed abundance of provender, notwithstanding all the destructive influences to which they are exposed, they multiply excessively during their journey, having families still more numerous and more frequently than in their usual homes. The progress may last from one to three years, according to the route taken, and the distance to be traversed until the sea-coast is reached, which in a country so surrounded by water as the Scandinavian peninsula must be the ultimate goal of such a journey. This may be either the Atlantic or the Gulf of Bothnia, according as the migration has commenced from the west or the east side of the central elevated plateau. Those that finally perish in the sea, committing what appears to be a voluntary suicide, are only acting under the same blind impulse which has led them previously to cross smaller pieces of water with safety.

_Cuniculus._[346]—Cranial and incisive characters those of _Myodes_, in the main, but the molars more of an Arvicoline type, the first upper one differing from that of all other members of the family in having seven prisms. Externally of the general shape of _Myodes_, but distinguished by the absence of external ears, the shortness and dense furring of the feet, the obsolete pollex with rudimentary nail, and the great length of the two middle claws of the manus. Represented by one species, the Banded Lemming (_C. torquatus_), of the Arctic region.

Remains of both _C. torquatus_ and _Myodes lemmus_ occur in British Pleistocene deposits.

_Fiber._[347]—Closely allied to _Arvicola_, both externally and in cranial and dental characters, but with the tail nearly as long as the body (apart from the head), compressed, nearly naked, and reticulate. Feet incompletely webbed, and the whole body adapted for a thoroughly aquatic life.

The Musk-Rat or Musquash (_F. zibethicus_, Fig. 209) is the only representative of this genus, and the largest member of the subfamily, the head and body being about 12 inches in length. It is rather a heavily built animal, with a broad head, no distinct neck, and short limbs; the eyes are small, and the ears project very little beyond the fur. The fore limbs have four toes and a rudimentary thumb, all with claws; the hind limbs are larger, with five distinct toes, united by short webs at their bases. The tail is laterally compressed, nearly naked, and scaly. The hair much resembles that of a beaver, but is shorter; it consists of a thick soft under-fur interspersed with longer stiff, glistening hairs, which overlie and conceal the former on the upper surface and sides of the body. The general colour is dark umber-brown, almost black on the back and gray below. The tail and naked parts of the feet are black. The musky odour from which it derives its name is due to the secretion of a large gland situated in the inguinal region, and present in both sexes.

[Illustration: FIG. 209.—The Musk-Rat (_Fiber zibethicus_.)]

The Musk-Rat is peculiar to America, being extensively distributed in suitable localities in the northern part of the continent, extending from the Atlantic to the Pacific, and from the Rio Grande to the barren grounds bordering the Arctic Seas. It is aquatic in its habits, living on the shores of lakes and rivers, swimming and diving with great facility, feeding on the roots, stems, and leaves of water-plants, or on fruits and vegetables which grow near the margin of the streams it inhabits. Musk-Rats are most active at night, spending the greater part of the day concealed in their burrows dug out of the bank, consisting of a chamber with numerous passages, all of which open under the surface of the water. For winter quarters they build more elaborate houses of conical or dome-like form, composed of sedges, grasses, and similar materials plastered together with mud. As their fur is an important article of commerce, large numbers are annually killed, being either trapped or speared at the mouths of their holes.

The skull of the Musk-Rat is shown in Fig. 203 (p. 459); its structure is essentially Arvicoline, but the squamosals are greatly expanded, with a corresponding reduction of the parietal and interparietal, and the interorbital constriction of the frontals attains its greatest development. Fossil remains of _Fiber_ occur in the North American Pleistocene.

_Neofiber._[348]—This genus, while agreeing with _Fiber_ in the characters of the skull and teeth, differs by the cylindrical tail, and the normal form of the feet, in which the toes are not bent laterally at an angle with the sole. The single species _N. alleni_, commonly known as the Round-tailed Musk-Rat, is found in Florida, and is much less completely aquatic in its habits than _Fiber_. Its colour is brown above, and silvery-white mixed with rufous below, the sides of the body gradually shading from brown to rufous, the forehead and the tip of the nose are black, while the tail is rufous mingled with black.

Subfamily =Siphneinæ=.—Includes two genera of Mole-like Rodents with an _Arvicoline_ dentition, but with the body thoroughly adapted for a subterranean life, the limbs and tail being very short, and the external ears rudimentary. Both are Palæarctic.

_Ellobius._[349]—The Russian _E. talpinus_, the typical representative of the genus, has short claws, and comes nearest to the _Arvicolinæ_. _E. fuscocapillus_ is from Afghanistan.

[Illustration: FIG. 210.—_Siphneus armandi._ (From Milne-Edwards.)]

_Siphneus._[350]—This genus (Fig. 210) includes species inhabiting Northern and Central Asia, and is characterised by the great length of the claws of the manus. Remains of an existing species occur in the Pleistocene of the Altai, while an extinct one has been described from the Pliocene of North China.

Subfamily =Deomyinæ=.—Represented only by the under-mentioned genus, in which the bituberculate anterior and tricuspidate middle ridge of the first upper molar presents a condition intermediate between that obtaining in the _Cricetinæ_ and that of the _Murinæ_.

_Deomys._[351]—Externally as in _Mus_. Pollex with a narrow nail; hind feet elongate. Infraorbital vacuity of skull triangular, not narrowed below. Upper incisors with a pair of minute grooves. First upper molar with seven distinct tubercles, of which three are placed on the middle ridge, and two on each of the others. One species, _D. ferrugineus_, from the Lower Congo, an animal about the size of the Common Mouse.

Subfamily =Murinæ=.—Molars rooted and tuberculated; those of the upper jaw with three longitudinal rows of tubercles (Fig. 206, _A_).

This group includes the true Rats and Mice, and may be regarded as more specialised than the _Cricetinæ_. All the members of the group closely resemble one another, and are light and active, with large ears, bright eyes, and long and scaly tails. Their coloration, in conformity with the fossorial and nocturnal habits of most of the forms, is sombre, and their movements are remarkably agile and graceful.

[Illustration: FIG. 211.—The Australian Brown-footed Rat (_Mus fuscipes_). After Gould.]

_Mus._[352]—Incisors narrow, without grooves. Structure of molars as in Fig. 206, _A_ (p. 463). Incisive foramina of skull long; coronoid process of mandible well developed. Ears and eyes large; muzzle naked at the extremity. Fur soft, in some cases intermingled with spines. Pollex with a short nail in place of a claw. No cheek-pouches. Tail long, nearly naked, with rings of overlapping scales. Vertebræ: C 7, D 13, L 6, S 4, C 26-32.

This genus is the largest in the whole mammalian class, comprising not less than 130 species, ranging over the whole of the Old World, with the noteworthy exception of Madagascar. On the whole, the species are more numerous in tropical than in temperate regions, and very few occur in cold countries. Many of the species living in warm climates have flattened spines mingled with the fur; these spines being shed in winter, when a warmer covering is necessary, and replaced by hair. Five species occur in England, which are briefly noticed below; and it may be observed that none of the species are much larger than _M. decumanus_ or smaller than _M. minutus_. As a rule the habits of the species are similar to those of the English forms, but a few are arboreal, while others again, like the one represented in Fig. 211, are aquatic. The earliest known representatives of the genus (excluding _Acanthomys gaudryi_ of the Lower Pliocene Pikermi beds of Attica) occur in the Pleistocene of Europe.

[Illustration: FIG. 212.—_A_, Head of Brown Rat (_M. decumanus_). _B_, Head of Black Rat (_Mus rattus_).]

The Brown or Norway Rat (_M. decumanus_) is a heavily built animal, growing to 8 or 9 inches in length, with a bluff rounded head, small ears (Fig. 212, _A_), and a comparatively short tail, which is always shorter than the head and body combined, and generally not longer than the body alone. The colour is a uniform grayish-brown above and white below, the ears, feet, and tail being flesh coloured. Black varieties, which are often mistaken for true Black Rats, are by no means rare, but the differences in size and proportions form a ready means of distinguishing the two. The Brown Rat is believed to be a native of Western China, where a race (_M. humiliatus_) has been discovered so like it as to be practically indistinguishable. Both this, and the next species agree in their predaceous habits, omnivorous diet, and great fecundity. They bear four or five times in the year from four to ten blind and naked young, which are in their turn able to breed at an age of about six months; the time of gestation being about twenty days.

The Black Rat (_M. rattus_) is a smaller and more lightly built species, generally not more than 7 inches in length, with a slender head (Fig. 212, _B_), large ears, and a thin tail of about 8 or 9 inches in length. The colour is usually a glossy bluish-black, somewhat lighter below; but in the tropical variety described as _M. alexandrinus_ the general colour is gray or rufous, and the belly white. The disposition of the Black Rat is milder than that of _M. decumanus_, and the white and pied rats kept as pets mostly belong to this species. In many localities where it was formerly abundant it has been entirely superseded by _M. decumanus_, but it is said that in some parts of Germany it has been lately reasserting itself.

_M. musculus_, the Common House-Mouse, is, like the Brown Rat, originally a native of Asia, whence it has spread to all the inhabited parts of the globe. Its habits and appearance are too well known to need any description.

_M. sylvaticus_, the Wood or Long-tailed Field-Mouse, is very common in many parts of England, often taking to barns and outhouses for shelter during the winter. It is of about the same size and proportions as _M. musculus_, but of a bright reddish-gray colour, with a pure white belly.

_M. minutus_, the Harvest-Mouse, is the smallest of the European Mice, seldom exceeding 2½ or 3 inches in length. It is of a yellowish-red colour, with comparatively short ears and tail. It lives entirely away from human habitations, generally dwelling in grass or corn-fields, where it builds a globular nest of dried grass of the size of a cricket-ball, in which the young are nurtured.

_Nesocia._[353]—General characters those of _Mus_, but the incisors and molars very much wider, and the tubercles of the latter more connected by transverse ridges, thus producing a laminated type of structure.

This genus has been placed by some writers in a distinct subfamily with _Phlœomys_, but Mr. O. Thomas regards it as so closely allied to _Mus_ that even its generic separation may be open to question. It comprises several species, mostly spread over Southern Asia, ranging from Palestine to Formosa, and from Kashmir to Ceylon, but _N. scullyi_ is found in Turkestan. The great Indian Bandicoot-Rat (_N. bandicota_) is the largest representative of the subfamily, often exceeding a foot in length. _N. bengalensis_ is remarkable for possessing no less than eighteen mammæ. Fossil remains of _Nesocia_ occur in the Pleistocene of Madras and in the Pliocene of Northern India; those from the first-named deposits being referable to existing species.

_Golunda._[354]—Like _Mus_, but with a distinct groove down the front of the upper incisors. There are only three species, one from Western India, one from West Africa, and the other from Eastern Africa.

_Uromys._[355]—Differs from _Mus_ in having the scales of the tail not overlapping, but set edge to edge, so as to form a sort of mosaic work. There are about six species of _Uromys_, spread over the northern part of the Australian region from the Aru Islands to Queensland.

_Chiruromys._[356]—Externally like _Mus_, but with the terminal portion of the tail without scales above, quite naked, transversely wrinkled, and prehensile. Scales of remainder of tail more or less pentagonal, and arranged in oblique diagonal series. Supraorbital vacuity of skull without projecting plate in external wall. Incisive foramina short and narrow; auditory bulla small. Upper molars very complex, with the tubercles (of which there are eleven in the first tooth) low, and distinctly arranged in transverse rows. Known only by _C. forbesi_, from mountains in New Guinea, which must be regarded as a specialised form very similar in outward appearance to _Uromys cervinipes_.

_Hapalotis._[357]—Hind limbs elongated. Incisive foramina very large. No coronoid process to the mandible. This genus is confined to Australia, where there are about fifteen species known. They are pretty little animals, with long ears and tail, and in many respects resemble the Jerboas, whose place they seem to take in the sandy Australian deserts. Remains of _H. albipes_ occur in the Pleistocene of New South Wales.

_Mastacomys._[358]—Like _Mus_, but with the molars remarkably broadened, and with only four mammæ. The single species of the genus is as yet only known from Tasmania, though it has been found fossil in New South Wales; it is somewhat similar in size and general appearance to the English Water-Vole, but has much longer and softer fur.

_Acanthomys._[359]—Fur almost entirely composed of flattened spines. Teeth and skull as in _Mus_, but the coronoid process of mandible very small. There are six species of Spiny-Mice known, all of about the size of the Common Mouse. They are found in Syria, Palestine, and Eastern Africa as far south as Mozambique. _A. dimidiatus_ presents the appearance of a little Hedgehog when its spines are erected; it inhabits the stony deserts of Arabia Petræa and Palestine, and feeds on bulbs. A fossil Mouse (_A. gaudryi_) referred to this genus occurs in the Lower Pliocene of Attica.

_Echinothrix._[360]—A very remarkable rat with an extremely elongated muzzle, all the bones of the face being much produced. The incisors are faintly grooved. The only species is _E. leucura_, an animal of about the size of the Brown Rat, with its fur thickly mixed with spines. It is found in Celebes.

_Typhlomys._[361]—This genus is represented by a single species from China, which resembles a House-Mouse in size and general appearance, but has smaller ears, while the eyes are so reduced in size as to be totally concealed by the long eyelashes.

_Cricetomys_[362] and _Saccostomus_.[363]—These two African genera have been—from the presence of cheek-pouches—usually placed in the neighbourhood of _Cricetus_, but their molars are of the Murine type. _Cricetomys_ is said to have grooved upper incisors, and is represented only by _C. gambianus_. There are two species of _Saccostomus_.

_Pithechirus._—A small Rodent from Sumatra and Java described under this name is a true Mouse, having nothing to do with _Chiropodomys_, to which it has been compared.

_Family_ SPALACIDÆ.

Mole-like forms, with very small or rudimentary eyes and ear-conchs, large claws, and short or rudimentary tail. Form cylindrical. Incisors large; premolars present or absent; molars rooted, with re-entering enamel-folds; palate narrow.

Subfamily =Spalacinæ=.—Angular part of the mandible arising from the lower edge of the socket of the lower incisor. No premolars.

_Spalax._[364]—Represented by the great Mole-Rat (_S. typhlus_) of South-Eastern Europe, in which the eyes are completely covered by the skin.

_Rhizomys._[365]—Eyes uncovered, although very minute; small naked ear-conchs; and a short partially hairy tail. Includes several species from Northern India, Tibet, China, Burma, Malaya, and Eastern Africa. A fossil species occurs in the Pliocene Siwaliks of Northern India.

Subfamily =Bathyerginæ=.—Angular part of the mandible arising from the side of the socket of the lower incisor. Premolars absent or present. Confined to the Ethiopian region.

_Bathyergus._[366]—Upper incisors strongly grooved; _p_ ¹⁄₁, _m_ ³⁄₃; no ear-conchs; very powerful claws. One species (_B. maritimus_), from South Africa, attaining a length of about 10 inches.

_Georychus_[367] and _Myoscalops_.[368]—Upper incisors without grooves. _Georychus_, with some half dozen species, generally has _p_ ¹⁄₁; _Myoscalops_, with one species, usually has _p_ ³⁄₃, and the second toe of the foot is the longest. In _Georychus_ the premolar may be wanting, and some examples of _Myoscalops_ have only two teeth of this series.

_Heterocephalus._[369]—Small and nearly naked forms, with small head, small eyes, no ear-conchs, moderately long tail, and powerful fore feet provided with a pair of large pads; _p_ ⁰⁄₀, _m_ ²⁻³⁄₂₋₃. Two species. These very remarkable little Rodents are regarded by Mr. O. Thomas as very closely allied to _Georychus_, but specialised, and, so to speak, somewhat degraded for a purely subterranean life, for which their hairless body is peculiarly adapted. They are found in Somali-land, where they burrow in the sandy soil.

_Family_ GEOMYIDÆ.[370]

Terrestrial or fossorial forms, with large cheek-pouches opening on the cheeks outside the mouth. Squamosal much expanded, and the jugal extending forwards to the lachrymal. _P_ ¹⁄₁; molars rooted or rootless, with transverse laminæ. Nearctic and Neotropical regions.

Subfamily =Geomyinæ=.—Incisors broad; mastoid not appearing on the top of the skull; eyes small; ear-conch rudimentary; limbs short, subequal. Habits fossorial.

_Geomys._[371]—Upper incisors deeply grooved. The common North American Pouched-Rat or “Pocket-Gopher” (_G. bursarius_) inhabits the plains of the Mississippi and lives in burrows. Several other species are recognised from the Southern United States, Mexico, and Central America. The genus is represented in the Pleistocene and Pliocene of the United States.

_Thomomys._[372]—Upper incisors plain. Represented by two species, with numerous varieties found all over Canada and North America west of the Rocky Mountains. Remains referred to an existing species occur in the Pliocene of Oregon. _Entoptychus_, from the Miocene of the United States, is an allied genus, with broad incisors and rootless molars.

Subfamily =Heteromyinæ=.—Incisors narrow; mastoid appearing largely on the top of the skull; eyes and ears moderate or large; hind limbs and tail elongated. Habits terrestrial.

_Dipodomys._[373]—This genus is characterised by the rootless molars. It is best known by _D. phillipsi_, the Kangaroo-Rat of the desert regions east of the Rocky Mountains, having habits like those of the Jerboas. The typical forms have four toes in the pes; but in others, which it has been proposed to separate as _Dipodops_, there are five: _D. ordi_ and _D. agilis_ belong to the latter group.

_Perognathus_[374] and _Heteromys_.[375]—In both these genera, which are represented by species of very small size, the molars are rooted; the latter being distinguished by the presence of flattened spines mingled with the fur, and having species ranging into South America. According to Dr. C. H. Merriam the forms described as _Cricetodipus_ are not separable from _Perognathus_; while Dr. Coues considers that _Saccomys_ was founded upon a species of _Heteromys_. _Pleurolichus_, from the Miocene of the United States, is regarded as an extinct genus allied to _Heteromys_.

_Family_ DIPODIDÆ.

Terrestrial forms usually with four upper cheek-teeth, and typically with the following characters. Incisors compressed; molars with transverse enamel-folds; infraorbital vacuity of skull (Fig. 7, p. 37) large and rounded; jugal ascending in front to the lachrymal; and the mastoid part of the auditory bulla usually very large.

Subfamily =Sminthinæ=.—Molars rooted; _p_ ¹⁄₀, _m_ ³⁄₃. Skull with the infraorbital vacuity widest below, and the incisive palatal foramina long. Limbs short. Palæarctic.

_Sminthus._[376]—Represented by the Rat-like _S. vagans_ from Northern Europe and Asia, in which the ears are rather long and pointed, the tail is covered with short hairs and nearly as long as the body, while the molars present a somewhat complicated pattern. This genus has generally been regarded as an aberrant member of the _Muridæ_, but was transferred in 1887 to the present family by Dr. H. Winge.

Subfamily =Zapodinæ=.—Molars rooted; _p_ ¹⁄₁, _m_ ³⁄₃; cervical vertebræ free; hind limbs elongated; metatarsals separate; hind feet with five digits. Nearctic region.

_Zapus._[377]—The American Jumping-Mouse (_Z. hudsonianus_) extends over almost the whole North-American continent from Labrador to Mexico.

Subfamily =Dipodinæ=.—Molars rooted; _p_ ⁰⁻¹⁄₀₋₁, _m_ ³⁄₃; cervical vertebræ more or less ankylosed; hind limbs elongated; metatarsals united; hind feet with only three functional digits. Palæarctic and Ethiopian regions.

This subfamily includes the true Jerboas, and contains three genera: _Dipus_[378] with three toes, and _Alactaga_[379] and _Platycercomys_[380] with five, the outer two not reaching to the ground. The latter is distinguished by the absence of premolars, and comprises many species extending from Siberia to Nubia.

Remains of the existing _Alactaga decumana_[381] occur in the Pleistocene of Germany, and those of _Zapus hudsonianus_ in the corresponding strata of the United States. _Platycercomys_ has been recorded from the Pleistocene of Northern Asia.

Subfamily =Pedetinæ=.—Molars rootless; cervical vertebræ free; hind limbs elongated; metatarsals separate; hind feet with four digits. Vertebræ: C 7, D 12, L 7, S 3, C 30. Ethiopian region.

_Pedetes_,[382] the Cape Jumping-Hare (_P. caffer_), by far the largest species of the family, extends from Mozambique and Angola to the Cape of Good Hope.

_Section_ HYSTRICOMORPHA.

Skull (Fig. 213) with a stout zygomatic arch; jugal not supported below by a continuation of the maxillary zygomatic process; infraorbital vacuity large; mandible with the angular part arising from the outer side of the bony socket of the lower incisor. Clavicles perfect or imperfect; fibula distinct. One premolar in each jaw.

_Family_ OCTODONTIDÆ.

Clavicles complete. Skull with long incisive foramina extending into the maxillæ; and usually an inferior angle to the jugal. Molars with external and internal enamel-folds; _p_ ¹⁄₁, except in _Ctenodactylus_. Mammæ placed high up on the sides of the body. Confined to the Ethiopian and Neotropical regions, with the exception of one species of _Echinomys_ which ranges into Central America. Habits mostly terrestrial, but occasionally fossorial or natatorial.

Subfamily =Ctenodactylinæ=.—Molars semi-rooted; jugal as in _Dipodidæ_; the two inner toes of the hind feet with a horny comb and rigid bristles. Ethiopian region.

_Ctenodactylus._[383]—Represented only by _C. gundi_ from North Africa, on the borders of the Sahara. Has no premolars; each foot has four digits; the hind limbs are rather longer than the fore; the ears small; and the tail reduced to a stump. This animal is about the size of the Water-Vole, and dwells on rocky ground, its habits being diurnal. The peculiar comb-like inner toes are employed for dressing the fur.

[Illustration: FIG. 213.—Skull of _Hydrochœrus capybara_ (reduced).]

_Pectinator._[384]—Closely allied to the preceding, but with a minute premolar in each jaw; and a moderately long and bushy tail. One species (_P. spekei_), from Somali-land.

Subfamily =Octodontinæ=.—Molars semi-rooted or rootless, with simple enamel-folds; fur soft. There are some six existing genera, including Rat-like species, all of which are South American, except _Petromys_, which is Ethiopian.

_Octodon._[385]—Upper and lower molars alike; ears moderate; tail of medium length and tufted. Vertebræ: C 7, D 12, L 7, S 4, C 25. Typically represented by _C. cumingi_ of Chili and Peru, with other species from Chili and Bolivia. They live in large communities.

_Habrocoma._[386]—Lower molars more complex than the upper; ears large; and fur extremely soft. Two Bolivian species.

_Schizodon._[387]—One species, inhabiting elevated spots in the Southern Andes, and characterised by the enamel-folds of the upper molars meeting in the middle line. The external characters are much the same as in _Ctenomys_, but the ears are larger and the claws shorter.

_Ctenomys._[388]—Incisors broad; molars rootless, with kidney-shaped crowns; last molar small and cylindrical; eyes and ears very small; claws larger than the toes. Some four species. Fossil remains are common in the Pleistocene of Buenos Ayres and the cavern-deposits of Brazil. Habits fossorial.

_Spalacopus._[389]—Represented by two Chilian species, distinguished from the preceding genus by the rudimentary ears. These rodents store up magazines of food in their burrows.

_Petromys._[390]—The South African _P. typicus_ is closely allied to _Spalacopus_, but differs by its harsh fur, the shortness of the pollex, and the somewhat bushy tail. The teeth are semi-rooted, with single inner and outer enamel-folds, nearly meeting in the middle.

Subfamily =Echinomyinæ=.—Molars semi-rooted or rootless, with deep and curved enamel-folds; fur more or less harsh, frequently mixed with spines; tail generally long. One Ethiopian genus, and the remaining nine or so Neotropical. Many of the species are of large size, some being arboreal and others aquatic.

_Myopotamus._[391]—Incisors very large; molars with two internal and two external enamel-folds in the upper, and three internal and one external in the lower jaw, last molar the largest; ears moderate; tail about two-thirds the length of the head and body, scaly, and sparsely haired; hind feet webbed; five digits. Vertebræ: C 7, D 13, L 6, S 4, C 25. The well-known Coypu (_M. coypu_), the only existing representative of this genus, is one of the largest living members of the order, and attains a length of about 2 feet. It is common in South America, living in burrows near water, and feeding on aquatic plants. Fossil remains of the genus occur in the caverns of Brazil, as well as in the Tertiaries of Argentina.

_Capromys._[392]—This genus comprises arboreal forms from the West Indies allied to the Coypu, but, according to Dr. G. E. Dobson, showing signs of affinity with the _Hystricidæ_. The incisors are smaller than in the Coypu, and the upper molars have one internal and two external enamel-folds; the ears are comparatively small; the tail usually of considerable length, and the general form somewhat Rat-like. The typical _C. pilorides_ is somewhat smaller than the Coypu, and is confined to Cuba; it is remarkable for the subdivision of the lobes of the liver into a number of lobules. _C. brachyurus_ and _C. prehensilis_ are also confined to Cuba. In Jamaica the genus is represented by _C. melanurus_, which is somewhat smaller than a Rabbit, and has no secondary lobulation of the liver.[393]

_Aulacodus._[394]—Upper incisors with three deep grooves; molars as in _Capromys_. Fur very harsh; tail moderate, sparsely haired; manus with rudimentary pollex, and small fifth digit; pes with no hallux, and rudimental fifth digit. One species (_A. swinderianus_), from Western and Southern Africa, which attains a length of nearly 2 feet, and dwells in burrows.

_Plagiodon._[395]—Allied to _Capromys_, but with the enamel-folds of the molars very complex, and forming a kind of zig-zag pattern in those of the upper jaw. Represented only by _P. ædium_ of Hayti and Jamaica.

_Loncheres_[396] and _Echinomys_.[397]—These genera include small South American species, in most of which flattened lanceolate spikes are mingled with the fur. The majority of the species occur in Guiana and Brazil, but one species of _Echinomys_ has been recorded from Central America. Fossil remains of both genera occur in the cavern-deposits of Brazil.

_Mesomys._[398]—This genus resembles _Loncheres_ externally, but the pollex has a short curved claw, and there are no spines in the fur.

_Dactylomys._[399]—A Brazilian genus presenting the following distinctive features. Ears short; tail long and scaly; pollex minute; third and fourth digits of manus elongated, with short convex nails. Incisors flat; molars divided into two lobes, each of which has a single enamel-fold. Represented by two species, _D. typus_ and _D. amblyonyx_, both of which seem to be rare and but little known. In the elongation of some of the digits _Dactylomys_ recalls _Chiromys_ among the Primates.

_Cercomys._[400]—This South American genus is usually placed near _Carterodon_, from which it is readily distinguished by the pointed muzzle and the plain incisors.

_Carterodon._[401]—This genus, which was originally described upon the evidence of skulls from the Brazil caves, but subsequently found living, is readily distinguished by the broad and grooved incisors. The upper molars have one inner and two outer enamel-folds; those of the lower jaw being the reverse of this.

_Fossil Forms._—Remains of the existing genus _Loncheres_ occur in the Brazilian cave-deposits, which also yield the extinct _Dicolpomys_. A large number of fossil _Octodontidæ_ from the Tertiaries of South America have been described under many generic names, but it will be sufficient to mention that _Phloramys_ and _Pithanotomys_ are considered to be allied to _Ctenomys_; while _Morenia_, _Orthomys_, and _Trilodon_ show affinity to _Myopotamus_. _Pellegrinia_, from the Pleistocene of Sicily, may be allied both to _Ctenodactylus_ and _Octodon_.

_Family_ THERIDOMYIDÆ.

This extinct family, which is represented in the Tertiaries of Europe and the United States, comprises several genera of comparatively small Rodents, which are regarded by Dr. Schlosser as nearly related to the _Octodontidæ_, although connected by _Archæomys_ with the _Chinchillidæ_. The dental formula is the same as in the _Octodontidæ_. In the typical genus _Theridomys_, from the Lower Miocene and Upper Eocene of Europe, the molars are rooted, and have three or four re-entering enamel-folds, which form isolated discs on the worn crowns. _Syllophodus_, from the Miocene of the United States, is closely allied. _Protechinomys_ and _Trechomys_ are genera from the Phosphorites of Central France with rooted molars; while in _Archæomys_ of the same deposits the molars are rootless, with the enamel-folds dividing their crowns into laminæ, as in the Chinchillas.

_Family_ HYSTRICIDÆ.

Build stout. Limbs subequal. A number of long and stout spines in the integument. Facial portion of skull short and broad, and the jugal without an inferior angle. Molars with external and internal enamel-folds; completely or partly rooted.

Subfamily =Synetherinæ=.—Molars rooted; clavicles complete; upper lip not cleft; soles tuberculated; pollex absent; four mammæ; tail generally prehensile; spines mixed with long hairs. This group is confined to America, all the forms except one being arboreal, and their habits less strictly nocturnal than in the next subfamily. There are three genera.

_Erethizon._[402]—Represented by the common Canadian Porcupine (_E. dorsatus_), a stout heavily-built animal, with long hairs almost or quite hiding the spines; four anterior and five posterior toes; and a short stumpy tail. It is a native of the greater part of Canada and the United States where there is any remnant of the original forest left. Remains of _Erethizon_ occur in cavern-deposits in Pennsylvania.

[Illustration: FIG. 214.—The Tree Porcupine (_Synetheres prehensilis_).]

_Synetheres._[403]—This genus contains some eight or ten species, known as Tree Porcupines (Fig. 214), found throughout the tropical parts of South America, and one of them extending northwards into Mexico. They are of a lighter build than the Ground Porcupines, are covered with short, close, many-coloured spines, often mixed with hairs, and their tails are always prehensile. Their hind feet have only four toes, owing to the suppression of the hallux; but they have a peculiar fleshy pad on the inner side of the foot, between which and the toes boughs and other objects can be firmly grasped as with a hand. Vertebræ: C 7, D 17, L 5, S 3, C 36. An extinct species of this genus has been described from the cavern-deposits of Brazil.

_Chætomys._[404]—Distinguished by the shape of its skull and the greater complexity of its teeth. It contains only one species (_C. subspinosus_), a native of the hottest parts of Brazil.

Subfamily =Hystricinæ=.—Molars semi-rooted; clavicles incomplete; soles smooth; a rudimentary pollex: six mammæ; tail not prehensile. Now confined to the Old World, where they occur in Southern Europe, Africa, India, and the Malay Archipelago as far eastwards as Borneo. Habits terrestrial and nocturnal. Three genera.

[Illustration: FIG. 215.—The Common Porcupine (_Hystrix cristata_).]

_Hystrix._[405]—This genus is readily characterised by the inflated skull, in which the nasal chamber is often considerably larger than the brain-case, and by the short tail, tipped with numerous slender stalked open quills, which make a loud rattling noise when the animal moves. Vertebræ: C 7, D 15, L 4, S 4, C 12. The best-known member is the Common Porcupine (_H. cristata_, Fig. 215), which occurs throughout Southern Europe and North and West Africa, but is replaced in South Africa by _H. africæ-australis_, and in India by the Hairy-nosed Porcupine (_H. leucura_).

The following account of the habits of the last-named species is from Dr. Jerdon: “_Hystrix leucura_ is found over a great part of India, from the lower ranges of the Himalayas to the extreme south, but does not occur in lower Bengal, where it is replaced by _H. bengalensis_. It forms extensive burrows, often in societies, in the sides of hills, banks of rivers and nullas, and very often in the dams of tanks, and in old mud walls, etc. In some parts of the country they are very destructive to various crops, potatoes, carrots, and other vegetables. They never issue forth till after dark, but now and then one will be found returning to his lair in daylight. Dogs take up the scent of the Porcupine very keenly, and on the Nilghiris I have killed many by the aid of dogs, tracking them to their dens. They charge backwards at their foes, erecting their spines at the same time, and dogs generally get seriously injured by their strong spines, which are sometimes driven deeply into the assailant. The Porcupine is not bad eating,—the meat, which is white, tasting something between pork and veal.”

Besides these three large crested species of _Hystrix_, there are four or five smaller species without nuchal crests occurring in North-East India and in the Malay region, from Nipal to Borneo.

Fossil species of _Hystrix_ occur in the Pleistocene and Pliocene of India, and in Europe from the Upper Pliocene to the Middle Miocene, being perhaps also represented in the French Phosphorites. Remains from the Pliocene and Miocene of the United States have been referred to this genus, and if rightly determined are of especial interest from a distributional point of view.

_Atherura._[406]—The Brush-tailed Porcupines are much smaller animals than the last, characterised by their long tails tipped with bundles of peculiar flattened spines. Of the three species two are found in the Malay region and one in West Africa. A fossil species occurs in the cavern-deposits of Madras.

_Trichys._[407]—This genus contains but one Bornean species (_T. guentheri_), externally very like an _Atherura_, but differing from the members of that genus in many important cranial characters.

_Family_ CHINCHILLIDÆ.

Terrestrial forms, with elongated hind limbs, bushy tails, very soft fur, and complete clavicles. Jugal without an inferior angle, and extending forwards to the lachrymal; palate contracted in front and deeply emarginate behind; incisors short, and the molars divided by continuous enamel-folds into transverse laminæ. Neotropical region. This family includes only three existing species, divided into as many genera.

_Chinchilla._[408]—In this genus the fore feet have five and the hind four digits, the tail is long and bushy, and the auditory bullæ are enormous, appearing on the top of the skull. The one species (_C. lanigera_) is restricted to the alpine zones of the Andes from the north of Peru to the south of Chili. It is a Squirrel-like Rodent, about 10 inches in length, the tail somewhat exceeding 5 inches, and the ears very large. Its fur is greatly valued on account of its extreme softness and delicate gray colour.

_Lagidium_[409] and _Lagostomus_.[410]—_Lagidium_ has four digits in both fore and hind feet, and _Lagostomus_ three only in the hind feet, and the auditory bullæ are much smaller than in the preceding genus. _Lagidium_ has the same distribution as _Chinchilla_; while _Lagostomus_, as represented by the Viscacha (_L. trichodactylus_), is found in the Pampas from the Uruguay River to the Rio Negro. The Viscachas live in burrows, generally in large numbers, and are nocturnal in their habits. Remains referable to the existing species, as well as others which appear to belong to extinct forms, occur in the Pleistocene deposits of South America.

_Extinct Genera._—Several Rodents from the South American Tertiaries more or less closely allied to _Lagostomus_ have been described by Dr. Ameghino under the names of _Prolagostomus_, _Pliolagostomus_, etc. The huge _Megamys_ (_Potamarchus_), from the infra-Pampean deposits of Parana and Patagonia, is referred to this family, and has dimensions approximating to those of an Ox. Other fossil genera have received the names of _Epiblema_ and _Tetrastylus_.

_Family_ CASTOROIDIDÆ.

_Castoroides._[411]—The large Beaver-like Rodent with the dimensions of a Bear from the Pleistocene of the United States described under this name is regarded by Dr. Coues as the type of a family. Its dentition is nearest to that of _Chinchilla_ and _Hydrochœrus_, but some of the cranial characters are like those of the _Castoridæ_. The genera _Amblyrhiza_ and _Loxomylus_, from the Pleistocene of the Antilles, appear to be allied types.

_Family_ DASYPROCTIDÆ.

Terrestrial forms with subequal limbs, hoof-like claws, short or obsolete tail, and rudimentary clavicles. Mandibular masseteric ridge obsolete; palate broad; incisors long; molars semi-rooted, with external and internal enamel-folds. Neotropical region.

_Dasyprocta._[412]—Includes several slender-limbed species, with three hind toes, commonly called Agoutis, inhabiting Central and South America, one (_D. cristata_) extending into the West-Indian Islands. Numerous fossil remains of this genus occur in the cavern-deposits of Brazil.

_Cælogenys._[413]—This genus is readily characterised by the presence of five hind toes, and the extraordinary development of its zygomatic arches, which are enormously expanded vertically, forming great convex bony capsules on the sides of the face, enclosing on each side a large cavity lined with mucous membrane, and communicating by a small opening with the mouth. The Paca (_C. paca_) is about 2 feet long, and, like the species of _Dasyprocta_, lives generally in the forests or along the banks of rivers. This species appears to date from the epoch of the Pleistocene deposits of the Brazilian caves. A smaller species from Ecuador, living at elevations of from 6000 to 10,000 feet, has been described as _C. taczanowskii_.

_Family_ DINOMYIDÆ.

Distinguished from the _Dasyproctidæ_ by the cleft upper lip, rather long and bushy tail, the presence of four digits in both fore and hind feet, and the complete clavicles. The manubrium is broad; the optic foramina are confluent; the incisors broad; and the molars rootless, with enamel-folds dividing them into transverse laminæ.

_Dinomys._[414]—The sole representative of this family is the Rodent known as _D. branicki_, of which hitherto only a single specimen has been obtained. This was captured in Peru, where it was found at daybreak walking about a courtyard; the inhabitants of the district were previously unacquainted with the species, from which its extreme rarity may be inferred. Externally it resembles much the Paca, having similar S-like nostrils; but in the laminated molars, and many features of the skeleton, it differs from all the other Rodents with hoof-like nails. It is regarded by its describer, the late Professor Peters, as a connecting link between the _Octodontidæ_, _Chinchillidæ_, _Dasyproctidæ_, and _Caviidæ_.

_Family_ CAVIIDÆ.

Terrestrial or natatorial forms, with short incisors, strong mandibular masseteric ridges, long and curved paroccipitals, and palate contracted in front. Fore feet with four digits, hind feet with three. Clavicles imperfect. Molars divided by enamel-folds into transverse laminæ; milk-teeth shed before birth. Other characters as in _Dasyproctidæ_. Neotropical region.

_Cavia._[415]—Limbs and ears short, subequal; tail none. Vertebræ: C 7, D 13, L 6, S 4, C 7. This genus includes several species widely distributed throughout South America, extending even to the Straits of Magellan. The Restless Cavy (_C. porcellus_), which is found throughout Uruguay and Brazil, has been very generally regarded as the ancestral form of the domesticated Guinea-Pig. It is about 10 inches long, and weighs a little over a pound; its fur is long and of a nearly uniform grayish-brown colour. This species is rarely found in dry sandy localities, preferring marshes covered with aquatic plants, among which it lies concealed, feeding in the early morning and after sunset in the evening; but when the soil is dry it forms burrows. It lives in societies of from six to eighteen individuals, breeding but once a year, with one, or at most only two, young at a birth. The Guinea-Pig (probably a misnomer of Guiana-Pig) is larger than _C. porcellus_, and is regarded by Dr. Nehring as descended from another species, _C. cutleri_. It is white in colour, with irregular patches of reddish-brown and black. The Bolivian Cavy (_C. boliviensis_), found throughout the higher regions of Bolivia, usually at an elevation of 10,000 or 12,000 feet, is exceedingly shy, and lives in burrows, which in some districts are so numerous as to have completely undermined the soil. The Rock-Cavy (_C. rupestris_), distinguished by its short, blunt nails, is found in rocky situations throughout Brazil, and is much sought after for its flesh. The Southern Cavy (_C. australis_), common along the coast of Patagonia, forms deep burrows, with several outlets, in sandy declivities. Remains of existing species of _Cavia_ are found in the cavern-deposits of Lagoa Santa, Brazil.

_Dolichotis._[416]—Characterised by the great length of the ears and the short tail. The palate is so much contracted in front that the premolars of opposite sides touch by their antero-internal edges. Vertebræ: C 7, D 12, L 8, S 3, C 10.

The Patagonian Cavy (_D. patachonica_)—the only living representative of the genus—is rather larger than a Hare, which it somewhat resembles in external appearance. It inhabits the dry sterile districts of Patagonia and La Plata, disappearing wherever the country becomes more humid. This animal burrows in the earth, although in districts where the Viscacha is found it is said to avail itself of the works of the latter. Unlike other cavies, its eyes are protected from the glare of the sun by prominent eyelashes. The body is covered with a long dense fur of a rusty colour. Two young are produced at a birth. Three species of _Dolichotis_ have been described from the Brazilian cave-deposits, one of which is probably not really separable from the existing form.

_Hydrochœrus._[417]—A large aquatic form with all the feet fully webbed; the skull (Fig. 213, p. 481) large, with enormous paroccipital processes; and the molars very complex, the third upper one having some twelve transverse laminæ. Upper incisors grooved. Vertebræ: C 7, D 14, L 6, S 3, C 8.

The Capybara (_H. capybara_) is the largest existing Rodent, and the only living representative of the genus. It is a bulky and stoutly built animal, and attains a length of about 4 feet. The body is covered with long and coarse hair, reddish-brown above and brownish-yellow beneath. Capybaras are found over the whole of the eastern part of South America, and to the westward range into Bolivia and Peru. They frequent the borders of rivers and lakes, concealing themselves among reeds and other water plants. Remains of _Hydrochœrus_ are found in the cavern-deposits of Brazil, which are probably referable to the existing species; one extinct species from the Pleistocene of Buenos Ayres is estimated to have attained a length of 5 feet, while _H. magnus_ of the same deposits was of still larger dimensions. The genus is also represented in the Pleistocene of South Carolina and the infra-Pampean beds of Parana.

_Extinct Genera._—A number of South American fossil Rodents have been referred to extinct genera of _Caviidæ_. Thus _Plexochœrus_, from the Tertiary of Argentina, differs from _Hydrochœrus_ in having only nine laminæ in the last upper molar; _Cardiomys_, _Cardiatherium_, etc., from the infra-Pampeans are also stated to be allied to _Hydrochœrus_, while _Contracavia_, of the same deposits, is related to _Cavia_, but of larger size. _Microcavia_, again, from the Pleistocene of Argentina, is regarded as connecting _Cavia_ with _Dolichotis_. The Tertiary European genera _Issiodoromys_ and _Nesocerodon_ are apparently referable to the present family.

_Suborder_ DUPLICIDENTATA.

Two pairs of incisors in the upper jaw (the second very small, and placed directly behind the large first pair), the enamel of which extends round to their posterior surfaces. At birth there are three pairs of these incisors, but the outer one on each side is soon lost. Incisive foramina large; and usually confluent; bony palate very narrow from before backwards; no true alisphenoid canal; fibula ankylosed to the tibia, and articulating with the calcaneum. Testes permanently external. This suborder includes the Picas, Hares, and Rabbits, all of which are strictly terrestrial.

_Family_ LAGOMYIDÆ.

Complete clavicles, subequal limbs, no external tail, and short ears. Skull depressed, frontals contracted and without postorbital processes; _p_ ¹⁄₁ or ²⁄₂; molars rootless, with transverse enamel-folds. Palæarctic and Nearctic.

_Lagomys._[418]—Represented by about a dozen species of small Guinea-Pig-like animals, inhabiting chiefly the mountainous parts of Northern Asia (from 11,000 to 14,000 feet), one species only being known from South-East Europe, and another from the Rocky Mountains.

The Picas, or Tailless Hares, live in holes among the rocks of their native mountains, and are agile and shy little creatures. The genus is well represented through the upper and middle Tertiaries. It has been proposed to separate those fossil forms with _p_ ²⁄₁ as _Myolagus_, and those with _p_ ¹⁄₁ as _Titanomys_, but this seems scarcely advisable.

_Family_ LEPORIDÆ.

Imperfect clavicles, elongated hind limbs, short recurved tail, and long ears. Skull (Fig. 216) compressed, frontals with large wing-shaped postorbital processes _p_ ³⁄₂; molars as in the _Lagomyidæ_. Cosmopolitan (except Australasia). Vertebræ: C 7, D 12, L 7, S 4, C 13-15.

[Illustration: FIG. 216.—Skull of Hare (_Lepus timidus_).]

_Lepus._[419]—The single genus _Lepus_ includes about twenty species, all of which resemble one another in general external characters. In all the fore limbs have five and the hind only four digits, and the soles of the feet are densely clothed with hairs similar to those covering the legs; the inner surface of the cheeks is also hairy. Although the family has such a wide distribution, the greater number of the species are restricted to the Palæarctic and Nearctic regions, only a single species (_L. brasiliensis_) extending into South America, where it has existed since the date of the Pleistocene deposits of the Brazilian caves.

The Common Hare (_L. timidus_[420]) may be taken as a typical example of the genus, and is characterised by the great length of the ears and hind limbs. It is found in all parts of Europe except the north of Russia, the Scandinavian peninsula, and Ireland. Its fur is usually of a tawny gray colour above and white beneath, with the upper surface of the short tail and the tips of the ears black. The colour of the fur differs, however, considerably in different latitudes and at different seasons of the year; showing a tendency to become white during winter in northern countries, while assuming a reddish-yellow hue in the more genial climate of southern Europe. The Hare is a nocturnal animal, remaining during the day on its “form,” as the slight depression is called which it makes in the open field, usually among grass.

[Illustration: FIG. 217.—The Common Hare (_Lepus timidus_).]

The Mountain Hare (_L. variabilis_) is found throughout the northern part of the Palæarctic region, ranging from Ireland in the west to Japan in the east, and also occurring in several of the more southerly mountain ranges, such as the Pyrenees, the Alps, and the Caucasus. It is smaller than the common species, with a smaller and more rounded head, and shorter ears, tail, and hind limbs. In cold climates the colour of the whole animal changes in the winter to a pure white (as in Fig. 218), with the exception of the tips of the ears, which remain black. In Ireland no winter change of colour takes place.

[Illustration: FIG. 218.—The Mountain Hare (_Lepus variabilis_).]

The Rabbit (_L. cuniculus_), speaking of the wild race only, is distinguished from the Hare externally by its smaller size, shorter ears and feet, the absence or reduction of the black patch at the tip of the ears so characteristic of the Hare, and by its grayer colour. The skull is smaller and lighter, with a slenderer muzzle and a longer and narrower palate. Besides these characters, however, the Rabbit is sharply separated from the Hare by the fact that it brings forth its young naked, blind, and helpless; to compensate for this, it digs a deep burrow in the earth in which they are born and reared, while the young of the Hare are born fully clothed with fur, and able to take care of themselves in the “form” in which they are born. The weight of the Rabbit is from 2½ to 3 lbs., although individuals perfectly wild have been recorded up to more than 5 lbs. Its general habits are too well known to need a detailed description here. It breeds from four to eight times a year, bringing forth each time from three to eight young. Its period of gestation is about thirty days, and it begins to breed when six months old. It attains to an age of about seven or eight years.

[Illustration: FIG. 219.—The Rabbit (_Lepus cuniculus_).]

The geographical distribution of the Rabbit presents many most interesting peculiarities. It is believed to be originally a native of the western half of the Mediterranean basin only, and still abounds in Spain, Sardinia, Southern Italy, Sicily, Greece, Tunis, and Algeria; and many of the Islands adjoining these countries are quite overrun with it. Thence it has spread, partly by man’s agency, northwards throughout temperate Western Europe, increasing rapidly wherever it gains a footing; and this extension is still going on, as is shown by the case of Scotland, in which sixty years ago Rabbits were little known, while they are now found in all suitable localities up to the extreme north. It has also gained admittance into Ireland, and now abounds there as much as in England. Out of Europe the same extension of range has been going on. In New Zealand and Australia Rabbits, introduced either for profit or sport, have increased to such an extent as to form one of the most serious pests that the farmers have to contend against, as the climate and soil seem to suit them perfectly, and their natural enemies are too few and too lowly organised to keep their numbers within reasonable bounds. In other cases Rabbits introduced into islands have become or remained more or less distinct from their parent stock; thus the Rabbits both of the Falkland Islands and of Jamaica still show traces of their descent from domesticated varieties, and have never reverted to the ordinary brownish-gray type. And again, as was pointed out by Mr. Darwin,[421] the Rabbits in the island of Porto Santo, near Madeira, whose ancestors were introduced from Spain in 1418 or 1419, have formed quite a distinct diminutive race, barely half the bulk or weight of English Rabbits, and differing in certain slight details of colour and habits.

_Bibliography of Rodentia._—G. R. Waterhouse, “Observations of the Rodentia,” _Mag. Nat. Hist._ iii. (1839); Id. _Ann. Nat. Hist._ viii. and x. (1839-42); Id. “On the Geographical Distribution of the Rodentia,” _Proc. Zool. Soc._ 1839, pp. 162-174; Id. _Natural History of the Mammalia_, vol. ii. “Rodentia” (1848); Gervais, _Dic. Univ. d’Hist. Nat._ xi. p. 202 (1848); Brandt, “Untersuchungen über die craniologischen Entwickelungsstufen und Classification der Nager der Jetzwelt,” _Mém. de l’Acad. Impér. de St. Pétersbourg_ (1855); Lilljeborg, _Systematisk Œfversight af de Gnagnde Däggdjuren_, Upsala, 1866; Alston, “On the Classification of the Order _Glires_,” _Proc. Zool. Soc._ 1876, pp. 61-98; Trouessart, “Catal. de Rongeurs, Vivants et Fossiles,” _Bullet. Soc. d’Études Scient. d’Angers_, 1880-1881; Coues and Allen, “Monographs of North American Rodentia,” _United States Geol. Surv. of Territories_, vol. xi. (1877); Winge, “Rodentia pa Lagos Santa, Brazil.” _Mus. Lund._ vol. iii. (1887); various papers by Peters in _Monatsber. Ak. Berlin_, and by Alston, Anderson, Blanford, Dobson, Milne-Edwards, Thomas, and others, in _Proc. Zool. Soc._, _Journ. Asiat. Soc. Beng._, _Ann. Mag. Nat. Hist._, etc.