Fig. 280.—Right lateral aspect of the anterior portion of the cranium of Erinaceus collaris. Enlarged. (From Dobson, Proc. Zool. Soc. 1881, p. 403.)
The Insectivora comprise a number of comparatively small mammals, generally of terrestrial, although rarely of arboreal or aquatic habits, and presenting the following common features. They are unguiculate, and have plantigrade or subplantigrade, and generally pentadactylate feet, in which the pollex and hallux are not opposable to the other digits. They are diphyodont and heterodont, and the teeth are rooted. The molars are studded with sharp cusps, the crowns of the upper molars being either quadrangular or triangular; there are never less than two incisors in either side of the mandible; and in many cases the incisors, canines, and anterior premolars are not clearly differentiated from one another (Fig. 280); the canines being usually weak. Clavicles are present, except in Potamogale. The body is clothed with fur or protected by an armature of spines; the testes are inguinal or placed near the kidneys, and are not received into a scrotum; the penis is pendent or suspended from the wall of the abdomen; the uterus is two-horned and with or without a distinct corpus uteri; the placenta is discoidal and deciduate; and the smooth cerebral hemispheres do not extend backwards over the cerebellum (Fig. 281). The projection of the muzzle far beyond the extremity of the lower jaw is a very general feature. The humerus generally has an entepicondylar foramen. Certain forms, such as Talpa and Galeopithecus, are unique among mammals in having ossified intercentra in the dorso-lumbar region of the vertebral column.
Representatives of this order are found throughout the temperate and tropical parts of both hemispheres (except South America and Australia), and exhibit much variety both in organisation and in habits. With the exception of the Tupaiidæ, all are nocturnal; the greater number are cursorial, but some (Talpa, Chrysochloris, Oryzorictes) are fossorial; some (Potamogale, Nectogale, Myogale) are natatorial, and a few (Tupaiidæ) arboreal; while the species of the aberrant genus Galeopithecus glide through the air like the Flying Squirrels. To the great majority the term insectivorous is strictly applicable, Galeopithecus alone being phytophagous; while Potamogale is said to feed on fish, and the different species of Moles live chiefly on worms. The general organisation of the Insectivora indicates a very low type, and were it not for the specialised character of their placentation and the tendency to lose the differentiated characters of the anterior teeth they might be regarded as closely allied to the ancestral type of many of the heterodont mammals. The strongly marked distinction of the canines from the incisors and anterior premolars in the Mesozoic and most of the Tertiary mammals (excepting some of the Ungulates) points, however, very decidedly to the conclusion that the want of definition between these teeth in many of the modern Insectivora is an acquired feature. Fossil forms apparently indicate a relationship on the one hand with the Creodont Carnivora, and on the other with the Lemuroid Primates; indeed it is in some instances impossible to say whether extinct genera are really Insectivores or Lemuroids.
Fig. 281.—Upper surface of the brain of Tupaia ferruginea. (From Garrod, Proc. Zool. Soc. 1879, p. 304.)
In most Insectivora the cranial cavity is of small relative size, and in none is the brain-case elevated to any considerable extent above the facial line. The facial part of the skull is generally much produced, and the premaxillary and nasal bones are well developed. The zygomatic arch is usually slender or deficient, the latter being the case in most of the species; and postorbital processes of the frontals are found only in the Galeopithecidæ, Tupaiidæ, and Macroscelididæ. The number of dorsal vertebræ varies from 13 in Talpa to 19 in Centetes; that of the lumbar from 3 in Chrysochloris to 6 in Talpa and Sorex; and of the caudal from the rudimentary series of 8 in Centetes to the 40 or more of Microgale. Not less variable are the characters of the vertebræ themselves; the spinous processes often being very long in one and short in another species of the same genus. In the Soricidæ and Myogale the neural arches of the cervical vertebræ are very slender. In the Soricidæ and Gymnura the four anterior vertebræ develop large single hypapophyses. In Galeopithecus the centrum of each vertebra supports posteriorly a pair of intercentral ossifications; while in Erinaceus, Myogale, and Talpa small oval ossicles are found on the inferior surfaces of the lumbar interspaces. In Erinaceus, owing to the thickness of the neural cord in the cervical region and its abrupt termination, the diameter of the neural canal in the cervical and first two dorsal vertebræ greatly exceeds that of any of the succeeding vertebræ. The sternum is variable, but generally narrow, bilobate in front, and divided into segments. The pectoral girdle presents some remarkable adaptive modifications, most fully expressed in Talpa, having relation to the use of the fore limbs in burrowing; but in the Golden Moles (Chrysochloris) the forearm and manus alone become specially modified for this purpose. In Galeopithecus and Macroscelides the bones of the forearm (radius and ulna) are distally united. The manus has generally five digits, but in Rhynchocyon and in one species of Oryzorictes the pollex is wanting, while in the true Moles it is extremely modified. The femur has, in most species, a prominent ridge below the greater trochanter representing a third trochanter. In Galeopithecus, Tupaia, Centetes, Hemicentetes, Ericulus, and Solenodon the tibia and fibula are distinct, but in all the other genera more or less united together. The pes usually possesses five digits (rarely four by reduction of the hallux); and in some forms, as in the leaping species (Macroscelides, Rhynchocyon), the tarsal bones are greatly elongated. The form of the pelvis, and especially of the symphysis pubis, varies within certain limits; and these differences have been proposed by Leche as a basis for the classification of the families. Thus in the Galeopithecidæ, Tupaiidæ, and Macroscelididæ there is a long symphysis; in the Erinaceidæ, Centetidæ, and Potamogalidæ the symphysis is short; and in the Soricidæ, Talpidæ, and Chrysochloridæ there is none.
Space does not admit of attempting a sketch of the modifications of the muscular system, which will be found fully described in Dr. Dobson’s Monograph, referred to in the bibliography. As to the nervous system, it has been already mentioned that the brain throughout the order presents a low type of organisation; in none of the members do the cerebral hemispheres present any trace of convolutions, nor do they extend backwards so as to cover the cerebellum, while the olfactory lobes are large and project in front, and the corpus callosum is short and thin. In the Hedgehogs (Erinaceus) the spinal column ends abruptly opposite the third or fourth dorsal vertebra in a slender filament, and the dorsal and lumbar nerves, given off in front of this point, are carried backwards in two compressed bundles occupying the suddenly narrowed spinal canal as far as the sacrum.
Owing to the similarity in the character of the food, the truly insectivorous species, forming more than nine-tenths of the order, present little variety in the structure of their digestive organs. Except in Galeopithecus the stomach is a simple, thin-walled sac; but in some, as in Centetes and allied genera, the pyloric and œsophageal openings are very close together. The intestinal canal has much the same calibre throughout, and varies from three (in the Shrews) to twelve times (in the Hedgehogs) the length of the head and body. In the arboreal genera, Galeopithecus and Tupaia, as well as in the Macroscelididæ, all of which probably feed in part on vegetable substances, most of the species possess a cæcum. The liver is deeply divided into lobes, the right and left lateral being cut off by deep fissures; and both the caudate and Spigelian lobes being generally well developed. The gall-bladder, which is usually large and globular, is placed on the middle of the posterior surface of the right central lobe.
In most of the members of the order (Soricidæ, Centetidæ, Chrysochloridæ) the penis is capable of being more or less completely retracted within the fold of integument surrounding the anus; in some (Galeopithecidæ, Talpidæ) it is pendent in front of the anus; while in others (Macroscelididæ, Erinaceidæ, Solenodontidæ) it is carried forwards and suspended from the abdominal wall. In the subfamily Centetinæ and Chrysochloris the testes lie immediately behind the kidneys, but in others more or less within the pelvis. During the rutting season they become greatly enlarged, forming protrusions in the inguinal region. Except in Rhynchocyon the uterine cornua are long and open into a short corpus uteri, which in many species (Soricidæ, Talpidæ, Centetidæ, Chrysochloridæ) is not separated from the vagina by a distinct os uteri. With the exception of Galeopithecus all Insectivora appear to be multiparous, the number of young at a birth varying from two to eight in Erinaceus, and from twelve to twenty in Centetes. The position of the mammary glands and the number of the teats vary greatly. Thus in Galeopithecus there are two pairs of axillary teats, and in Solenodon a single post-inguinal pair; but in most species they range from the thorax to the abdomen, varying from two pairs in Gymnura to twelve in Centetes. In Chrysochloris the thoracic and inguinal teats are lodged in deep cup-shaped depressions.
Odoriferous glands exist in many species. In most Shrews these glands occur on the sides of the body at a short distance behind the axilla, and their exudation is probably protective, since few carnivorous animals will eat the dead bodies of these creatures. In both species of Gymnura and in Potamogale large pouches are situated on either side of the rectum and discharge their secretions by ducts, opening in the first-named genus in front of, and in the latter within the margin of the anus. In Centetes the ducts of similarly situated racemose glands open by pores at the bottom of deep pits placed at either side of the anus.
The integument is thin, but in many species is lined by a muscular coat, which is probably more developed in the Hedgehogs (Erinaceidæ) than in any other mammal. In this family and the Centetidæ most of the species are protected by spines implanted in the panniculus carnosus muscle, and more or less replacing the fur of the upper surface of the body.
The order is usually divided into two suborders, but the very aberrant genus which constitutes the first might well be raised to ordinal rank. It has little in common with the true Insectivora, but as it certainly belongs to no other of the recognised mammalian orders it is retained among them chiefly to avoid the inconvenience of increasing the number of ordinal divisions for the sake of a single isolated form.
Upper and lower incisors compressed, multicuspidate, the lower deeply pectinated; fore and hind limbs connected by a broad integumentary expansion forming a parachute.
In addition to the characters given under the head of the suborder it may be mentioned that the orbit is nearly surrounded by bone, the zygomatic arches are well developed, the tympanic forms a bulla, the ulna is distally united with the radius, the tibia and fibula are distinct, the pubic symphysis is long, the penis is pendent, the testes are received into inguinal pouches, the mammæ are axillary, the uterus is two-horned, and there is a large cæcum.
Galeopithecus.[530]—Dentition: i ²⁄₃, c ¹⁄₁, p ²⁄₂, m ³⁄₃; total 34. Second upper incisor and canine with two roots. Two species—G. volans and G. philippinensis. The former, which is distinguished from the latter by the form of the upper incisors, has a total length of nearly 2 feet. The long and slender limbs are connected by a broad integumentary expansion extending outwards from the sides of the neck and body, and forming also a web between the fingers and toes as far as the base of the claws (Fig. 282); the hind limbs are further connected by a similar expansion passing outwards along the back of the feet to the base of the claws, and, inwardly, involving the long tail to the tip, forming a true interfemoral membrane, as in the Bats.
The two species of Flying Lemurs, as the representatives of this genus are commonly but erroneously called, live in the forests of the Malay Peninsula, Sumatra, Borneo, and the Philippine Islands, where they feed chiefly on the leaves and fruits of trees. Their habits are nocturnal, and during the daytime they cling to the trunks or limbs of trees, head downwards, in a state of repose. With the approach of night their season of activity commences, when they may be seen gliding from tree to tree supported on their cutaneous parachute, and they have been observed to traverse in this way a space of 70 yards with a descent of only about one in five.
Fig. 282.—Feet of Galeopithecus philippinensis.
Galeopithecus was referred by some of the older zoologists and anatomists to the Bats, and by others to the Lemurs, but Professor Peters’s view, that it belongs to neither of these orders, and should be considered an aberrant Insectivore, has been very generally accepted, although, as mentioned above, the association is by no means a close one. Besides differing from the Bats in the form of the anterior limbs and of the double-rooted outer incisor and canine, it also contrasts strongly with them in the presence of a large sacculated cæcum, and in the great length of the colon, which is so remarkably short in all the Chiroptera. From the Lemurs, on the other hand, the form of the brain, the characters of the teeth, the structure of the skull, and the deciduate discoidal placenta completely separate it. In a recent elaborate memoir on the myology and affinities of Galeopithecus Dr. Leche[531] considers that we have in this genus an indication of the mode in which the Insectivora were modified into the Chiroptera, although it is completely off the direct line of descent. The deeply pectinated crowns of the lower incisors of Galeopithecus are quite unique in the class, and the only approach to the double-rooted canine, except in Erinaceus and Talpa, is found among the Marsupials in Perameles, where the root of the canine is grooved.
Upper and lower incisors conical, unicuspidate or with basal cusps only, the lower not pectinated; limbs free, formed for terrestrial progression.
The following table gives a key to the distinctive characters of the existing families:—
The second section, in which the molars are of the primitive tritubercular type, should probably be regarded as containing the most generalised representatives of the order; and it is noteworthy that the whole of them are confined to Africa, Madagascar, and the West Indies, whereas most of the first section are widely distributed over the Palæarctic and Oriental regions. None of the existing families of the second section are known in a fossil condition, although it is suggested that the extinct Leptictidæ includes allied types.
Skull with comparatively large brain-case, orbit surrounded by bone, well-developed zygomatic arch, perforated jugal, and a tympanic bulla. Upper molar broad, with cusps arranged in a W. Pubic symphysis long; radius and ulna, and tibia and fibula separate; metatarsus only slightly longer than tarsus. Usually a short cæcum. Habits arboreal and diurnal. Confined to the Oriental region.
Fig. 283.—The Pentailed Tree-Shrew (Ptilocercus lowi). From Gray, Proc. Zool. Soc. 1848. ½ natural size.
Tupaia.[532]—Dentition: i ²⁄₃, c ¹⁄₁, p ³⁄₃, m ³⁄₃; total 38. Feet naked beneath, the sole furnished with projecting pads; claws moderate, curved, and sharp; head pointed; ears rounded; tail bushy, distichous, with short hair below. The Tree-Shrews, of which there are some nine species, are found in India, Burma, the Malay Peninsula, the Nicobars, Sumatra, Java, and Borneo. The species closely resemble one another, differing chiefly in size and in the colour and length of the fur. Their general appearance is very Squirrel-like. Their food consists of insects and fruit, which they usually seek in the trees, but also occasionally on the ground. When feeding they often sit on their haunches, holding the food, after the manner of Squirrels, between their forepaws.
Ptilocercus.[533]—Represented only by the Pentailed Tree-Shrew (P. lowi, Fig. 283) of Borneo, in which the tail is of extraordinary length, with the proximal two-thirds naked, and the remaining third furnished with a bilateral fringe of long hairs, from which the genus takes its name.
Extinct Genera.—An Insectivore from the Middle Miocene of France, described as Lantanotherium, is said to be nearly allied to Tupaia. The genus Parasorex, from strata of similar age, has the dental formula i ³⁄₃, c ¹⁄₁, p ⁴⁄₄, m ³⁄₃, and is regarded as connecting the present with the following family.
Skull with comparatively large brain-case, strong zygomatic arch, a tympanic bulla, orbit surrounded by bone, imperforate jugal, and usually no postorbital process. Molars broad, with four cusps arranged in a W. Pubic symphysis long; proximal end of tibia and fibula united; radius and ulna united or separate; metatarsus much longer than tarsus. A large cæcum. Habits terrestrial, saltatorial, and nocturnal. The family is confined to Africa.
Macroscelides.[534]—Dentition: i ³⁄₃, c ¹⁄₁, p ⁴⁄₄, m ²⁄₂₋₃; total 40 or 42. Distal extremity of radius and ulna united. Five digits in manus, and five or four in pes. This genus, which is taken to include Petrodromus, comprises ten species widely distributed throughout the African continent. All are closely related, resembling one another in general form, and even in the colour of the fur. They fall into two groups, distinguished by the presence or absence of a small third lower molar.[535] M. tetradactylus (Fig. 284), the type of the genus Petrodromus, differs from all the other species in the absence of the hallux, and of the third lower molar. These animals are commonly known as Jumping Shrews, and, like the following genus, have the muzzle much produced.
Rhynchocyon.[536]—Dentition: i ¹⁄₃, c ¹⁄₁, p ⁴⁄₄, m ²⁄₂; total 36. Upper incisor frequently shed in the adult. Radius and ulna distinct; hind limbs relatively shorter, and proboscis longer than in the type genus; four digits in each foot. Four closely allied species have been described from East Africa. The head and body of the type species measures about 8 inches in length; and the long tail is covered with a ringed skin, sparsely haired. Its habits are fossorial.
Fig. 284.—Macroscelides tetradactylus. × ½. (From Peters, Reise nach Mossambique.)
Skull with a small brain-case; no postorbital process; slender and occasionally imperfect zygomatic arch, and an annular tympanic, which does not form a bulla. Upper molars with four principal cusps and a small central median cusp. Acromion of scapula bifid; pubic symphysis short; radius and ulna free, but tibia and fibula united proximally. No cæcum; penis carried forward and suspended from the wall of the abdomen. Habits terrestrial. Found in the Palæarctic, Ethiopian, and Oriental regions.
Subfamily Gymnurinæ.—Palate completely ossified; pelvis very narrow; fur without spines.
Gymnura.[537]—Dentition: i ³⁄₃, c ¹⁄₁, p ⁴⁄₄, m ³⁄₃; total 44. This genus, if Hylomys is rightly included, is represented by the two species, G. rafflesi and G. suilla, from the Malay Peninsula and Indian Archipelago. The former has the appearance of a large Rat with a long tail and head and projecting mobile snout; the latter, which is much smaller, with a short tail and small third upper premolar, has long been known under the name of Hylomys suillus, and classed with the Tupaiidæ. Both species present a very generalised type of dentition, in this respect occupying an almost central position in the order. G. suilla is represented in Mount Kina-Balu, Borneo, by a variety characterised by the presence of a dark dorsal streak. Many zoologists prefer to retain Hylomys as a distinct genus.
Subfamily Erinaceinæ.—Palate imperfectly ossified; pelvis wide; fur with spines.
Erinaceus.[538]—Dentition: i ³⁄₂, c ¹⁄₁, p ³⁄₂, m ³⁄₃; total 36. The first pair of upper incisors (Fig. 285) are considerably larger than the others, and are widely separated from one another in the middle line; the canine is very similar to the third incisor; and, except in E. europæus (Fig. 285), each of these teeth is inserted by two distinct roots (Fig. 280, p. 610). The first lower incisor is large and proclivous. The number of vertebræ is C 7, D 15, L 6, S 3, C 11.
Fig. 285.—Right lateral aspect of the anterior portion of the skull of the Hedgehog (Erinaceus europæus). Enlarged. (From Dobson, Proc. Zool. Soc. 1881, p. 403.)
The Hedgehogs comprise nearly twenty species, distributed throughout Europe, Africa, and the greater part of Asia, but not found in Madagascar, Ceylon, Burma, Siam, the Malay Peninsula, or Australia. All the species resemble one another in the armature of spines investing the upper surface and sides of the body; and all possess the power of rolling themselves up into the form of a ball, protected on all sides by the strong spines; the dorsal integument being brought downwards and inwards over the head and tail, so as to include the limbs also, by the action of special muscles. The common Hedgehog (E. europæus) is the most aberrant species, differing from all the rest in the peculiarly shaped and single-rooted third upper incisor and canine (Fig. 285), and in its very coarse, harsh fur. The dentition of the long-eared North Indian form, E. collaris (Fig. 280), may be considered characteristic of all the other species, the only important differences being found in the variable size and position of the second upper premolar, which is very small, external, and deciduous in the Indian E. micropus and pictus. The former species, limited to South India, is further distinguished by the absence of the jugal bone. Of the African species, E. diadematus, with long frontal spines, is probably the commonest; while E. albiventris has been made the type of a separate genus on account of the total absence of the hallux.
The well-known European species feeds on insects, worms, slugs, mice, rats, lizards, snakes, etc., as well as on eggs, fruit, and roots. It hibernates during the winter. The young are usually produced in July or August in litters of not more than four, but there may be a second litter in October; and the period of gestation is believed not to exceed a month. The Indian, and probably also the African species, do not hibernate.
The existing E. europæus dates from the Pleistocene period, and extinct species of the genus are found in the Upper and Middle Miocene of the Continent.
Extinct Genera.—The French Lower Miocene genus, Palæoerinaceus, appears to be allied to Erinaceus, but is distinguished by the wider and completely ossified palate. In the Upper Eocene of Central France there are two genera, which appear to be most nearly allied to Gymnura, although connected by Palæoerinaceus with Erinaceus. Of these Necrogymnurus,[539] with which Cayluxotherium is apparently identical, has teeth like Gymnura, but an imperfectly ossified palate like Erinaceus; and the skull is remarkable for the peculiar rugose structure of the parietal and temporal regions. Comphotherium is distinguished by the presence of a cingulum to the lower molars, like that found in Gymnura.
Skull (Fig. 286) long and narrow, with no zygomatic arch or postorbital process, and the tympanic ring-like and not forming a bulla. Upper molars with the cusps arranged in a distinct W. No pubic symphysis. The tibia and fibula united. No cæcum. Habits usually terrestrial, rarely aquatic. Distribution extensive.
The Shrews are Rat-like or Mouse-like insectivores, with the body covered with hair, and the muzzle long and pointed. Their dentition (Fig. 286) is peculiar and characteristic. Thus the first upper incisor is large and hook-like, with a more or less developed basal cusp on the posterior border. Between this and the last premolar there are a variable number of small teeth, representing the other incisors, the canine, and the anterior premolars; although, owing to the early obliteration of the maxillo-premaxillary suture, their homology is exceedingly difficult to determine. Three molars are invariably present, of which the third is much the smallest. In the mandible there are always six teeth, but in one species of Myosorex there may be a seventh. The first lower incisor is usually directed horizontally forwards; the second incisor (formerly reckoned as the canine) is the smallest tooth of the series, the fourth premolar being slightly larger.
This family, which includes considerably more than half the representatives of the order, has a distribution coextensive with the latter. Many classifications of this difficult group have been attempted, but according to the latest proposal of Dr. Dobson,[540] the genera may be divided into two subfamilies, distinguished by the apparently trivial character of the colour of the teeth.
Fig. 286.—Left lateral view of the cranium and mandible of Sorex veræpacis. In the cranium—i, first incisor; c, fourth incisor; p, canine; m, fourth premolar: in the mandible—i, first incisor; c, second incisor; p, fourth premolar; m, first molar. (From Alston, Proc. Zool. Soc. 1877.)
Subfamily Soricinæ.—Summits of the teeth coloured red.
Sorex.[541]—Dentition: i ⁴⁄₂, c ¹⁄₀, p ²⁄₁, m ³⁄₃; total 32. Openings of male and female generative organs separated from the anal orifice; penis cylindrical or tapering; ear well developed; tail long, covered with equal or subequal hairs.
It has been shown by Brandt that the position of the premaxillo-maxillary sutures in the type of the genus is between the fourth and fifth tooth, so that it appears that we must regard this genus as differing from all other Eutherian mammals in having four upper incisors. Dr. Dobson, in his paper quoted, classes the tooth here reckoned as the upper canine with the premolar series in all the Shrews. Habits terrestrial. Species numerous, inhabiting the Palæarctic and Nearctic regions.
Of the two species found in the British Isles the Common Shrew (S. vulgaris, Fig. 287) is by far the most common in England, and is about the size of the House Mouse, to which it approximates in general form. The body is clothed with close long fur, very soft and dense, and varying in colour from light reddish to dark brown above, rarely speckled or banded with white. The under surface of both the body and the tail is grayish. The basal four-fifths of all the hairs above and beneath are dark bluish-gray; the hairs of the tail are less densely set and coarser. On each side of the body, at a point about one-third of the distance between the elbow and the knee, may be found, especially in the rutting season, a gland covered by two rows of coarse hairs. This secretes a peculiar fluid, on which the odour of the animal depends; this odour being evidently protective, and rendering the creature secure against the attacks of many predaceous animals.
The geographical range of the Common Shrew is exceedingly wide, extending eastwards through Europe and Asia (north of the Himalayas) to North America.
Fig. 287.—The Common Shrew (Sorex vulgaris).
The Lesser Shrew (S. pygmæus[542]) is far less common in England and Scotland, although more abundant in Ireland, where S. vulgaris is unknown. It is distinguished from the latter not only by its inferior dimensions, but also by the circumstance that the third upper incisor is not longer than the fourth, and by the considerably shorter length of the forearm and manus. This species extends through Europe and Asia as far as the inland of Saghalin. Both this and the preceding species generally live in wooded districts, making their nests under the roots of trees, or in slight hollows. The great mortality noticeable among the Shrews in the early part of the autumn is probably due to insufficiency of food. The breeding season extends from the latter part of April to the beginning of August. The young, which are blind, naked, and toothless at birth, are very quickly developed. The number in a litter is usually from five to seven, but may be as many as ten.
The Alpine Shrew (S. alpinus), which is restricted to the Alpine region of Central Europe, is slightly larger than the common species, from which it is distinguished by the longer tail, the length of which exceeds that of the head and body, by the fur being dark on both surfaces of the body, and also by the larger size of the upper canine.
In North America S. bendirei is by far the largest species of the genus; and, as in many other species of the same country, the fourth upper incisor is relatively small. In S. hoyi (separated by some writers as Microsorex), of the same country, this tooth is rudimentary.
Other North American Shrews, which are regarded by some zoologists as generically distinct under the name of Neosorex, are aquatic, and thus take the place of the Old World genus Crossopus. These are S. palustris of the Rocky Mountains and S. hydrodromus of Unalaska Island, both of which resemble Crossopus in having the feet provided with swimming fringes, but agree with the other species of Sorex in their dentition and the character of the tail. The former species is about the size of Crossopus fodiens, while the latter is scarcely larger than S. pygmæus.
Soriculus.[543]—Dentition: i ⁴⁄₂, c ¹⁄₀, p ¹⁻²⁄₁, m ³⁄₃; total 30, or rarely 32. Opening of male or female generative organs forming with the anal orifice a shallow cloaca. Ear and tail as in Sorex. First upper incisor with an internal cusp. Habits terrestrial.
This genus is the only representative in the Oriental region of the Soricinæ, which are otherwise confined to the Palæarctic and Nearctic regions. The Indian and Burmese species comprise S. nigrescens, S. caudatus, and S. macrurus.
Notiosorex.[544]—Dentition: i ³⁄₂, c ¹⁄₀, p ¹⁄₁, m ³⁄₃; total 28. Tail moderate; first upper incisor without an inner cusp; other characters as in Soriculus. Habits terrestrial.
This American genus is represented by S. crawfordi and S. evotis, which are found in Central America and Mexico, and are thus some of the most southerly representatives of the Shrews in that continent. Their external appearance is very similar to that of the Old World genus Crocidura.
Blarina.[545]—Dentition: i ⁴⁻³⁄₂, c ¹⁄₀, p ²⁄₁, m ³⁄₃; total 32 or 30. Ear truncated above; tail short; otherwise as in Soriculus. This group of so-called Earless or Short-tailed Shrews is mainly North American, the common forms being B. dekayi and B. brevicauda. The species vary considerably in size; and B. mexicana and micrura extend the range of the genus into Mexico and Guatemala. The following account of the habits of B. brevicauda is taken from Dr. Merriam’s Mammals of the Adirondack Region: “The rigours of our northern winters seem to have no effect in diminishing its activity, for it scampers about on the snow during the severest weather, and I have known it to be out when the thermometer indicated a temperature of -20° Fahr. It makes long journeys over the snow, burrowing down whenever it comes to an elevation that denotes the presence of a log or stump, and I am inclined to believe that at this season it must feed largely upon the chrysalides and larvæ of insects that are always to be found in such places.” Dr. Merriam has made the interesting discovery that the common short-tailed North American Shrew supplements its insectivorous fare by feeding on beech-nuts, which will account for the generally very worn state of the teeth in this species.
Crossopus.[546]—Dentition: i ³⁄₂, c ¹⁄₀, p ²⁄₁, m ³⁄₃; total 30. Opening of male or female generative organs enclosed within the same ring as the anal orifice; penis broad, with lateral processes. Ears small, not truncated. Tail long, with an inferior fringe of elongated hair; feet also fringed. Habits aquatic. The Palæarctic Water-Shrew (C. fodiens) is considerably larger than the Common Shrew, from which it is readily distinguished externally by its shorter and much broader muzzle, comparatively smaller eyes, and larger feet adapted for swimming,—the sides of the feet and toes being provided with comb-like fringes of stiff hairs. The tail is longer than the body, and possesses a well-developed swimming fringe of moderately long, regularly arranged hairs, which extend along the middle of the flat under surface from the end of its basal third to its extremity. The fur of the body is long and very dense, varying much in colour in different individuals, and this has given rise to descriptions of many nominal species; the prevailing shades are dark brown, almost black, above, and more or less bright ashy tinged with yellowish beneath; sometimes in the same litter there are individuals with the under surface more or less dark coloured. In the number as well as in the shape of the teeth the Water-Shrew differs from the Common Shrew: there is a premolar less on each side above; the bases of the teeth are much more prolonged posteriorly; and their cusps are much less stained brown, so that in old individuals with worn teeth they often appear altogether white. This species resembles the otter in its aquatic habits, swimming and diving with great agility. It frequents rivers and lakes, making its burrows in the overhanging banks, from which when disturbed it escapes into the water. Its food consists of insects and their larvæ, small crustaceans, and probably the fry of small fishes. It is generally distributed throughout England, is less common in Scotland, and as yet it has not been recorded in Ireland; specimens have been obtained from many parts of Europe, and also from Asia as far eastward as the Altai Mountains.
Subfamily Crocidurinæ.—Teeth completely white.
Myosorex.[547]—Dentition: i ³⁄₂, c ¹⁄₀, p ²⁄₁₋₂, m ³⁄₃; total 30 or 32. Penis cylindroid and tapering; male or female generative organs opening close to anal orifice, but not forming a cloaca. Ears well developed; tail long, clothed with equal or subequal hairs. Habits terrestrial.
This genus is typically represented by M. varius, a very small Shrew from the Cape, which is quite unique among the whole family in having a rudimental seventh pair of lower teeth.
Crocidura.[548]—Dentition: i ³⁄₂, c ¹⁄₀, p ²⁻¹⁄₁, m ³⁄₃; total 28 or 30. Male or female generative organs forming a short cloaca with the anal orifice. Tail long, with a mixture of long and short hairs. Other characters as in Myosorex. Habits terrestrial.
This Old World genus includes over seventy nominal species, which have been divided into four subgenera, C. aranea and C. suaveolens of Continental Europe, and C. cœrulea of India, being well-known forms. The species are very variable and difficult to discriminate. C. aranea has a very wide distribution, ranging from Central and Southern Europe to North Africa and Central Asia. The name Musk-Rat is popularly applied in India to C. cœrulea, which frequents houses at night, hunting round rooms for cockroaches and other insects, and occasionally uttering a sharp shrill cry. The strong musky odour of this animal arises from large glands situated beneath the skin of the side of the body, a short distance behind the fore limbs. This odour is so powerful and penetrating that it is popularly believed in India that if the animal runs over a corked bottle of wine or beer it will infect the fluid within. Jerdon says that certainly many bottles are met with quite undrinkable from the peculiar musky odour of their contents, but, rejecting the possibility of its passing through the glass, he attributes it to the corks having been infected previously to bottling, stating in corroboration of this view that he has never found the odour in liquors bottled in England.
Diplomesodon.[549]—Dentition: i ²⁄₂, c ¹⁄₀, p ¹⁄₁, m ³⁄₃; total 26. Tail moderate; soles of the feet hairy. Other characters as in Crocidura. Habits terrestrial.
This genus is represented only by D. pulchellus of the Kirghiz steppes, which is allied to the following form, although retaining the normal Shrew-like external contour.
Anurosorex.[550]—Dentition: i ²⁄₂, c ¹⁄₀, p ¹⁄₁, m ³⁄₃; total 26. Ear very short; tail rudimental or short; soles of feet naked. Other characters as in Diplomesodon.
The two species of this genus are Mole-like terrestrial forms, of which the typical A. squamipes occurs in Tibet, while A. assamensis is found in Assam. The latter species has the longer tail. The habits of both are probably fossorial.
Chimarrogale.[551]—Dentition: i ³⁄₂, c ¹⁄₀, p ¹⁄₁, m ³⁄₃; total 28. Penis broad, with lateral processes; male or female generative organs opening within the same integumentary ring as the anal orifice. Tail long, with an inferior fringe of elongated hairs; ears small; plantar callosities simple; toes free. Habits aquatic.
This genus includes C. himalayica of the Himalaya and C. platycephalus of Japan. Both have the feet fringed, and, together with the next genus, may be regarded as the eastern analogues of Crossopus among the red-toothed series; their structural resemblances to the latter, if Dr. Dobson’s classification is a natural one, being probably due to adaptation for a similar mode of life.
Nectogale.[552]—Dentition: i ³⁄₂, c ¹⁄₀, p ¹⁄₁, m ³⁄₃; total 28. External ears not forming a conch, valvular. Plantar callosities forming adhesive pads; toes webbed. Other characters as in Chimarrogale. Habits aquatic.