The Cambridge Natural History Part 39

_Hapalomys_, with but one species, is Burmese. _Pithecochirus_ is Javanese and Sumatran. _Conilurus_ (also known as _Hapalotis_) is a genus containing species which are termed Jerboa Rats, on account of their mode of progression. They are desert and Australian forms. There are sixteen species.

[Ill.u.s.tration]

FIG. 235.--Spiny Mouse. _Acomys cahirinus._ .

_Mastacomys_, with one species, is limited to Tasmania. _Uromys_, with some eight species, is from Queensland, and inhabits also the Aru Islands and the Solomon Islands. The Celebesian _Echiothrix_, or _Craurothrix_ as it should apparently properly be called, is another genus containing but a single species. _Golunda_ is both Oriental and Ethiopian, one species occurring in each region. The beautiful little striped Barbary Mice, _Arviacanthis_ (or _Isomys_), are African, north as well as tropical.

The genus _Saccostomus_ resembles the Hamsters in the presence of cheek pouches. Its teeth, however, are Murine. It agrees with _Steatomys_ in the comparatively short tail. The caec.u.m is rather long. {474}

SUB-FAM. 2. HYDROMYINAE.--The genus _Hydromys_,[341] of which there are several species, the best known being _H. chrysogaster_, is an exclusively Australian form, and is aquatic in habit. It is a foot or so in length, and has a fairly long tail. The fore- and hind-limbs are webbed, in correspondence with its habits. The Australian Water-Rat is black, with an admixture of golden-coloured hairs dorsally and golden colour below, with a lighter median stripe. The thumb is small, and the webbing of the hands is not so marked as is that of the feet. The molars are only two in each half of each jaw. The caec.u.m is rather small, the measurements of the alimentary ca.n.a.l being: small intestine, 895 mm.; large intestine, 278 mm.; caec.u.m, 70 mm. Allied to the last is _Xeromys_, a genus which is also Australian, but limited to Queensland. It has been established by Mr. Thomas,[342] who discovered that it has the same reduced formula as _Hydromys_. _Xeromys_, however, is not an aquatic animal, and has unwebbed feet.

In the Luzon highlands Mr. Whitehead has discovered, and Mr. Thomas quite recently described,[343] a number of peculiar Rodents. Of these the genera _Chrotomys_, _Celaenomys_, and _Crunomys_ are allied to the Australian and New Guinea _Hydromys_.

_Chrotomys whiteheadi_ is unusual among Muridae, in its coloration being marked by a pale stripe down the back. The creature is the size of the Black Rat (_Mus rattus_). It is terrestrial not aquatic in habit, in spite of its likeness to _Hydromys_. The molars, however, are 3/3.

_Crunomys fallax_ is more like _Hydromys_. It has, however, three molars, as in the last genus. But the skull has the flattened form characteristic of _Hydromys_ as opposed to _Mus_.

Like _Batomys_, _Celaenomys silaceus_ is also somewhat intermediate between _Hydromys_ and _Mus_. It is described as very Shrew-like in appearance, and has a very pointed muzzle. Its habits Mr. Whitehead is "quite unable even to guess at." Like _Hydromys_ and _Xeromys_ this Rodent has but two molars.

SUB-FAM. 3. RHYNCHOMYINAE.--The genus _Rhynchomys_, containing but one species, _Rh. soricioides_ (of Thomas), is also, as both its generic and specific names imply, a somewhat Shrew-like form in external aspect. The skull, too, is Insectivore-like in its {475} elongation, and the lower incisors are worn to needle-like points. The two molars are excessively minute, and thus the always large gap in the jaws is greatly exaggerated.

It is suggested that this Rat is an insect-eater, but nothing positive is known.

SUB-FAM. 4. GERBILLINAE.--The Gerbilles form another sub-family, Gerbillinae, of the Muridae, or a family, according to some. The best-known genus is _Gerbillus_, including the Gerbilles proper. These animals are Old World in range, belonging to the three regions of that part of the world.

There are a large number of species in the genus, over thirty. They have a Jerboa-like form, with rather long hind-limbs and a long and hairy tail.

But the hind- as well as the fore-feet are five-toed. The molar teeth have no trace of tubercles, but only transverse lamellae of enamel. The incisors are orange; they are white in _Dipus_. _Gerbillus pyramidum_ is 90 mm.

long, with a tail of 125 mm. The ears are long, 13 mm. The tail has longer hairs at the tip.

[Ill.u.s.tration]

FIG. 236.--Gerbille. _Gerbillus aegyptius._ .

_Psammomys_ is in some respects different. The tail is shorter than in _Gerbillus_; its length in an individual of 165 mm. was 130 mm. As in _Gerbillus_ there are four pairs of teats, two pectoral and two inguinal.

This genus is exclusively Palaearctic in range. _Meriones_ has a range co-extensive with that of _Gerbillus_.

_Pachyuromys_ is an Ethiopian genus with a short tail. As the generic name denotes, the tail is not only short but thick and fleshy.

SUB-FAM. 5. OTOMYINAE.--The allied genera, _Otomys_ and _Oreinomys_, are Ethiopian. _Otomys unisulcatus_ has a tail shorter than the body, the measurements of a female of this species being 137 mm. with a tail of 87 mm. The ear is long, whence the name; it measured in this specimen 20 mm.

{476}

SUB-FAM. 6. DENDROMYINAE.--The genus _Deomys_ is an African form, consisting of only one species from the Congo region. _D. ferrugineus_ has a reddish colour as its name implies; the soles are quite naked and the tail is long and slender. It is considerably longer than the body, measuring (minus a fragment of the tip) 172 mm., while the body is 125 mm.

long. The characters of the molar teeth, which are three, are intermediate in their form between those of the true Rats and those of the Hamsters.

_Dendromys_ is also Ethiopian in range. There are several species. _D.

mesomelas_ is a smallish creature, 60 mm. long, with a tail of 90 mm.

_Steatomys_ is another African genus, allied to the last. Its tail, however, is only half the length of the body. The two remaining genera are _Malacothrix_ and _Limacomys_. Their range is African.

SUB-FAM. 7. LOPHIOMYINAE.--Allied to the Hamsters is the singular East African genus _Lophiomys_, with only one species, _L. imhausi_, of Milne-Edwards.[344] The size is between that of a Rabbit and of a Guinea-pig. The stomach is curved and somewhat intestiniform. It has been termed the Crested Rat on account of the "prominent crest of stiff hair running down the back." The fingers and toes are five, and the very long tail is clad with hair longer than that upon the body generally. The pollex is rudimentary, and the hallux is opposable.

The most remarkable structural feature in this genus concerns the skull, and on account of this it has been regarded as the type of a separate family. The temporal fossa behind the eye is covered over by a complete bony plate, formed by a downgrowth of the parietal, meeting an upgrowth from the malar; this singular arrangement of the bones recalls the conditions which obtain in turtles. The whole skull, moreover, is covered with symmetrically disposed granulations, such as are found in no other mammal; it suggests rather the skull of certain fish. It is believed that the bony plate already referred to is not really a portion of the bones of which it appears to be a prolongation, but merely an ossification of fasciae in this region. The atlas is granulated like the skull; there are sixteen pairs of ribs and a feeble clavicle. The molars are three, and of a peculiar form. {477} They have, in the case of the first three, transverse ridges, from which stand up two sharp and long tubercles. The other teeth have two ridges. The incisors are pale yellow. The shape of the teeth and the smallness of the caec.u.m suggest that this Rodent is not so purely a vegetarian as others, and that it nourishes itself largely upon insects.

SUB-FAM. 8. MICROTINAE.--The Voles or Water-Rats form a distinct group of Murine animals, to which the sub-family name of Microtinae has been applied from the genus _Microtus_ (more generally known as _Arvicola_), a genus which includes the Water-Rat and Field-Voles of this country. This genus has short ears, and a short and hairy tail. Its build is stouter and clumsier than that of the Rats. The genus is confined to the Palaearctic and the Nearctic regions. In this country there are three species. The best known is the Water-Vole or Water-Rat, _M. amphibius_, which has been seen by most people, and which frequents streams, ponds, and ca.n.a.ls. The feet, curiously enough, are not webbed, which seems to argue the recent adoption of an aquatic life. Mr. Trevor-Battye has remarked that this animal, when swimming at leisure, uses its hind-limbs only, carrying the fore pair at the sides like a Seal. The Bank-Vole, _M. glareolus_, is rather a local species in this country. It is a terrestrial Vole, and burrows. The Field-Vole, _M. agrestis_, has become notorious on account of the "plagues," to which its immense numbers have on occasions given rise. It is the smallest species, and has a greyish-brown fur like the Water-Vole, the Bank-Vole being redder. To give an idea of the cost of the depredations of this animal, Mr. Scherren quotes[345] a farmer who gave evidence before the Agricultural Commission to the effect that, putting the damage of one Vole at two pence, the amount of loss suffered on a farm of 6500 acres in two years would be 50,000!

The genus _Fiber_ comes very near the last. It is a North American genus.

The hind-feet are slightly webbed; the tail is a trifle shorter than the body, and is compressed and scaly, with scattered hairs. The thumb is short, but with a fully-developed claw. As in the last genus, the small and large intestines are roughly of the same length, and the caec.u.m is about one-fourth of the length of either. It is known as the "Musquash." {478}

Of _Fiber zibethicus_, or rather a closely-allied form, _F. osoyoosensis_, from Lake Osoyoos near the Rockies, Mr. Lord writes[346] that it constructs for itself a house of bulrushes built up from the bottom in 3 or 4 feet of water. It is dome-shaped, and rises about a foot out of the water. "If a dead or badly-wounded duck be left on the pool, it is at once seized on, towed into the house, and doomed." Thus it appears that this Rodent, like so many others, is largely carnivorous. It has also been a.s.serted that it eats fish.

_Neofiber_ is an allied genus, North American in range. The species, _N.

alleni_, is compared, as regards outward form, with the Water-Vole, _M.

amphibius_. It has, however, a shorter tail.

Another very well-known member of this sub-family is the Lemming. The name, however, applies to two quite distinct genera. The genus _Cuniculus_, including the Banded Lemming, _C. torquatus_, is an inhabitant of North America, Siberia, and Greenland. The tail is short, its length being 12 mm.

as against a body length of 101 mm. The feet are furred beneath, a not unusual state of affairs in Arctic mammals. The ears are very slight. The thumb is well developed, and bears a claw.

In _Myodes_, on the other hand, which is not so markedly an Arctic animal, though occurring in both Palaearctic and Nearctic regions, the ears are rather bigger, though still smaller than those of _Microtus_. The under surfaces of the feet are similarly furred. The tail is also short. It is commonly said that the two genera are to be distinguished by the furred feet of _Cuniculus_, and by the absence of fur in the present genus. That, according to Tullberg, does not appear to be the case. The differences are thus so much reduced that it seems almost unnecessary to retain the two genera. The best known species of _Myodes_ is of course the Scandinavian Lemming, _M. lemmus_. This animal used to occur in this country in Pleistocene times (as did also _C. torquatus_), and recently Dr. Gadow has found remains with skins attached in caves in Portugal. It may still survive in the mountains of the Peninsula.

The actual habitat of the Lemming in Scandinavia is the great tablelands, 3000 feet high in the centre. The migrations do not take place with regularity; even twenty years may elapse before the appearance in cultivated lands of those countless {479} hordes so familiar (as far as their description is concerned) to everybody. The Lemmings do not return from their exodus. They die from various causes, including combats with one another. Their chief foes, however, are Wolves and Gluttons, Buzzards and Ravens, Owls and Skuas, which batten on the migrant hordes. Their sudden increase in numbers recalls the similar increase at times of the Field-Vole, to which reference has already been made.

_Ellobius_ is an Old-World genus, which leads a "Talpine" life, and has in consequence rudimentary external ears and very small eyes. The tail is short. Contrary to what might be expected from its mode of life, the claws upon the digits are not strong.

The remaining genera of Vole-like Murines are _Phenacomys_ and _Synaptomys_ from North America, and Siphneus from Palaearctic Asia. _Evotomys_ is one of those genera which are common to both the Palaearctic and the Nearctic regions, but the bulk of the species are North American.

SUB-FAM. 9. SIGMODONTINAE.--This is the name given to another sub-family of Murine Rodents, a group which includes the Hamsters in the Old World as well as a large number of South American genera of Rat-like animals. Of these latter there are a very large number, the bulk of the group being American.

The Hamsters, genus _Cricetus_, as it is usually called, although apparently the correct name is Hamster, are Old-World forms of Pouched Rats. The Common Hamster, _C. frumentarius_, is about 210 mm. long, with a tail of 58 mm. It has cheek pouches. The small and the large intestines are not very unequal in length, and the caec.u.m is fairly large, being about one-sixth to one-seventh of the length of either. It is a purely vegetable-feeding creature, and in Germany where it occurs (and from which language its vernacular name is derived), hibernates during the winter in its burrow, having previously surrounded itself with a great acc.u.mulation of food carried thither.

To North America are peculiar the genera _Onychomys_, _Sigmodon_, and _Peromyscus_. The genus _Sigmodon_, the Cotton Rats, reaches Central America, and even gets a little farther south. The other two genera, though mainly North American, also extend their range to the south. _Onychomys_ has hairy {480} foot-pads, a state of affairs which characterises a number of these Rodents.

The genera _Megalomys_, _Chilomys_, _Reithrodontomys_, _Eligmodontia_, _Nectomys_, _Rhipidomys_, _Tylomys_, _Holochilus_, _Reithrodon_, _Phyllotis_, _Scapteromys_, _Acodon_, _Oxymycterus_, _Ichthyomys_, _Blarinomys_, _Notiomys_ are South American forms. _Oryzomys_ and _Rheithrodontomys_ are common to both parts of the New World.

The genus _Ichthyomys_ is remarkable on account of its un-Rodent-like habits and of certain a.s.sociated structural changes. _I. stolzmanni_ was obtained from Mount Chanchamays in Peru at an alt.i.tude of 3000 feet; it is a habitual fish-eater, and lives in streams. Another species, _I.

hydrobates_, was formerly referred to _Habrothrix_. The skull shows likenesses to that of the Australian _Hydromys_; but the most marked characters of adaptation are those of the teeth and caec.u.m. The cutting edges of the upper incisors form a reversed [347] of obvious use in holding a slippery fish. The caec.u.m is much reduced, short, and narrow. The general Otter-like shape of the creature is largely due to its flattened head, though its "size and general proportions are much as in the common Black Rat."[348]

This sub-family contains a number of genera from Madagascar, viz.

_Brachytarsomys_, _Nesomys_, _Hallomys_, _Brachyuromys_, _Hypogeomys_, _Gymnuromys_, and _Eliurus_.

SUB-FAM. 10. NEOTOMINAE.--The last sub-family of the Muridae is that of the Neotominae, containing the North American genera _Neotoma_, _Xenomys_, _Hodomys_, and _Nelsonia_.

FAM. 3. BATHYERGIDAE.--This family contains several genera which consist of subterranean forms. All these Rodents agree in a number of characters, of which the princ.i.p.al are as follows:--

The eyes are very small, and the external ears are reduced to the merest fringe of skin round the aural aperture. The legs are short, as is the tail; the hair-covering is reduced--a reduction which finds its culmination in the nearly nude _Heterocephalus_. Being burrowing creatures, a number of other modifications in accordance with this mode of life are to be seen in their structure. The upper incisors stand out in front of the closed lips, and prevent the entrance of earth. For the same reason {481} the nostrils are small, and the forehead but little expanded between them.

The genus _Bathyergus_ contains but a single species, the Cape Mole-Rat, which is found in Southern Africa; it is of moderate size, not exceeding a small Rabbit in dimensions. On the fore-limbs are exceedingly long claws, of which that borne by the second finger is the longest, and the claw of the thumb the shortest. The hind-feet have by no means such long claws. The scratching and burrowing is naturally chiefly effected by the fore-limbs.

The small and large intestines are of equal length, and each is rather more than six times the length of the caec.u.m; in these measurements the present genus differs from the next.

_Georhychus._--Of this African genus there are about ten species. The claws are not so long as in the last genus, but there are, as in _Bathyergus_, four molar teeth on each half of each jaw. The intestinal measurements in an example of _G. capensis_ were: small intestine, 25 inches; caec.u.m, 4 inches; large intestine, 15 inches.

The genus _Myoscalops_ or _Heliphohius_ (also with an African range) has six back teeth on each side. A number of species sometimes referred to the last genus are placed here by Mr. Thomas. The claws are small.