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 Macroscelidida, 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 (Soricida, Centetida, Chrysochloride) the penis is capable of being more or less completely retracted within the fold of integument surrounding the anus; in some (Galeopithecida, Talpida) it is pendent in front of the anus ; while in others (Macroscelidida, Erinaceida, Solenodontidae) it is carried forwards and suspended from the abdominal wall. In the subfamily Centetine 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 (Soricida, Talpida, Centetida, Chrysochloride) 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 (Erinaceida) than in any other mammal. In this family and the Centetid 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.

Suborder DERMOPTERA.

Upper and lower incisors compressed, multicuspidate, the lower deeply pectinated; fore and hind limbs connected by a broad integumentary expansion forming a parachute.

Family GALEOPITHECIDE.

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-Dentition: i, c, på, m; 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

1 Pallas, Acta Acad. Sci. Imp. Petropolis, vol. iv. pt. 1, p. 208 (1780).

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.

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. Leche1 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

1 Ueber die Säugethiergattung Galeopithecus. Sv. Ak. Handl. vol. xxi. pt. xi. (1886).

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.

Suborder INSECTIVORA VERA.

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:

I. Upper molars broad, multicuspidate, with more or less well-defined W-shaped crowns.

A. Symphysis pubis long; generally a cæcum; cerebral cavity

comparatively large.

a. Orbit encircled by bone; metatarsus moderate; arboreal.

Tupaiide.

b. Orbit not encircled by bone; metatarsus greatly elongated; terrestrial. Macroscelidida.

B. Symphysis pubis short or none; no cæcum; cerebral cavity small; skull without postorbital processes.

a. First and second upper molars with a central fifth cusp. a'. Tympanic annular, not forming a bulla. Erinaceida,

b. No central fifth cusp to upper molars.

a. Tympanic annular, not forming a bulla; no zygomatic arch. Soricida.

b'. Tympanic forming a bulla; zygomatic arch developed. Talpida.

II. Upper molars narrow, with V-shaped crowns.

a. Tympanic annular, not forming a bulla; zygomatic arch imperfect.

a". No clavicles. Potamogalida.

b". Clavicles well developed.

a"". Skull constricted between the orbits; penis sus

pended. Solenodontida.

b". Skull not constricted; penis pendent, retractile.

Centetida.

b. Tympanic forming a bulla; zygomatic arch well developed.

Chrysochloride.

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 Palearctic 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.

Family TUPAIIDÆ,

Skull with comparatively large brain-case, orbit surrounded by bone, well-developed zygomatic arch, perforated jugal, and a tympanic

natural size.

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.

Tupaia.-Dentition: i, c, p, m; 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 1 Raffles, Trans. Linn. Soc. vol. xiii. p. 256 (1822).