Insectivora

INSECTIVORA, an order of placental mammals of small size, with a dentition adapted to an insect-diet. Nearly all mem bers of this order are nocturnal .and terrestrial, many, however, are fossorial or arboreal, and a few are aquatic. There are gen erally five toes, each terminating in a claw; the first toe is never opposable to the others in either the fore or hind limb. A full series of teeth, including temporary, or deciduous milk-molars is developed, and the cheek-teeth are crowned with sharp cusps as a rule. The typical number of teeth is 44, arranged as shown in the formula i.4, c.+, p. 4 i m. ; occasionally there is a fourth pair of molars, while the incisors may be reduced to two pairs above and one pair below. The skull is of a primitive type, with a small brain-case, tympanic bone generally ring-like instead of forming a bulla and vacuities are frequently present in the palate. With the exception of the African Potamogale, collar bones are always present, and a central bone is usually present in the carpus. The uterus is two-horned, the placenta, so far as is known, is deciduate and discoidal; the testes are abdominal or inguinal, and the teats usually numerous.

Representatives of this order are found throughout the temper ate and tropical parts of both hemispheres, with the exception of South America (where only a few shrews have penetrated) and Australia.

The stomach is a simple, thin-walled sac ; sometimes as in Centetes, the pyloric and oesophageal openings are close together. In the arboreal forms, which probably feed on vegetables as well as insects, most of the species possess a caecum.

Varieties of the Order.

All the members of the order appear to be highly prolific, the number of young varying from two to eight in the hedgehog, and from twelve to twenty-one in the Tenrec. Scent-glands exist in many species. In most shrews they occur on the sides of the body at a short distance behind the axilla, and their exudation is probably protective, as very few carnivorous animals will touch them. In both species of Gymnura and in Potamogale large pouches are situated on each 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 vent. In the Tenrec similarly situated glands discharge by pores, opening at the bottom of deep pits.

If Galeopithecus and Galeopterus are accepted as members of the Insectivora then the order may be split into two suborders, the Dermoptera and the Insectivora vera. The former contains only the two genera Galeopithecus and Galeopterus. For further information on these two interesting genera see the articles GALEOPITHECUS and GALEOPTERUS.

Insectivora Vera.

The Insectivora vera may be divided into nine families, which fall into two groups. The first of these, con taining the families Tupaiidae and Macroscelididae, is character ised by the full development of the union between the two halves of the pelvis. The orbit is either surrounded by bone (Tupaiidae) or is separated from the hinder part of the skull by a post-orbital process (Macroscelididae). Some authors regard the Tupaiidae as lowly organized members of the order Primates, but the pres ent writer is quite unable to consider the genus Tupaia and its near relations Anathana, Dendrogale, Urogale, Tana and Ptilo cercus, as representing anything more than a group of Insectivores. The Tupaiidae, which are confined to the Oriental region, are, however, in addition to the bony ring surrounding the orbit, dis tinguished by the large size of the brain. The dental formula is I.*, C.+, P.4, M. . The Tupaias or Tree-Shrews are in many ways very like squirrels; they are, however, distinguished by their pointed insectivorous faces and light coloured shoulder stripes. The typical genus contains a great number of species and sub species. T. ferruginea, from the Malay Peninsula and Islands, is bright chestnut-brown in colour with an olive-brown face and tail; the majority of the members of this genus do not exceed 35o mm. in total length. T. pictus, of Borneo, is a very hand somely coloured Tree-Shrew, chestnut and olive above, with buff shoulder stripes and a black dorsal stripe. From the Rhio Archipelago comes a deep chestnut coloured form known as T. castanea. T. minor is a very small species from Borneo, with a hind-foot of only 28 mm., and a total length of about 28o mm.

The closely allied genus, Anathana, is distinguished from Tupaia by the inner sides of the ears being more hairy, the larger size of the lower lobe of the ear, and the coarser nasal reticulations. The species come from India and Borneo. The genus Urogale, allied to Tupaia and Anathana, contains but a single species U. cylindura from the Philippine Islands, in general dimensions and appearance about as in the smaller Tupaias, the total length being 25o mm.

A number of handsomely coloured Tree-Shrews has recently been placed in the genus Tana. Included in this genus is a very brightly coloured species from Borneo and Sumatra, T. tana. T. dorsalis, from Borneo, is a smaller species, with a well-marked black dorsal stripe extending from the crown of the head to the base of the tail. The smallest members of this family are in cluded in the genus Dendrogale, the total length not exceeding 235 mm. These pigmy Tree-Shrews come from Annam, Cochin China, Cambodia and Siam.

The asiatic Pentailed Tree-Shrew

(Ptilocercus lowi) is usually included in this family, although it differs very markedly from all the other genera. The tail is very long, with the proximal two thirds naked, and the remaining third furnished with a feather like fringe. This species, the only representative of the genus, is found in Borneo, Sumatra and parts of the Malay Archipelago.