Erinaceus, including the Hedgehogs, is a widely distributed genus—Palaearctic, Oriental, and Ethiopian in range. There are about twenty species. The familiar spines distinguish the Hedgehogs from their allies, as also the fact that they possess but thirty-six teeth, the formula being I 3/2 C 1/1 Pm 3/2 M 3/3. There are fifteen or fourteen ribs, and the tail is very short, consisting of only twelve vertebrae. As in Gymnura there is no caecum. The upper canine has usually, as in other Erinaceidae, two roots, but not in E. europaeus, which is one of the most modified of Hedgehogs.
The Hedgehog is a more omnivorous creature than Gymnura. It eats not only insects and slugs, but also chickens and young game birds, and lastly vipers. Four, or in some cases as many as five or six, young are produced at a birth; they are blind, with soft and flexible white spines. In hot and dry weather Hedgehogs disappear; they come forth in rainy weather. The English Hedgehog, as is well known, hibernates. The Indian species do not. The Hedgehog is occasionally spineless, which condition may be regarded as an atavistic reversion.[[369]]
The Hedgehog has acquired the reputation of carrying off apples transfixed upon its spines. Blumenbach thus quaintly describes this and other habits of the animal, whose English name he gives as "hedgidog": "Il se nourrit des productions des deux règnes organisés, miaule comme un chat, et peut avaler une quantité énorme de mouches cantharides. Il est certain qu'il pique les fruits avec les épines de son dos, et les porte ainsi dans son terrier."[[370]]
The Miocene Palaeoerinaceus is so little different from Erinaceus that it is really hardly generically separable. Erinaceus is therefore clearly one of the oldest living genera of mammals.
Necrogymnura of the same epoch and the same beds (Quercy Phosphorites) is doubtless an ancestral form. The palate is
perforated as in Erinaceus (it is not so in Gymnura and Hylomys), but on the whole it comes nearest to Hylomys.
Fam. 2. Tupaiidae.—This family contains the genera Tupaia and Ptilocercus. Tupaia is Oriental in range, extending as far east as Borneo. There are a dozen or so of species, which are generally arboreal and have the outward aspect of Squirrels. It has been suggested that this is a case of mimicry, the animal gaining some advantage by its likeness to the Rodent. The name Tupaia, it should be added, means Squirrel, and the long-nosed Squirrel, Sciurus laticaudatus, is so extraordinarily like it that "one has to look at the teeth" to distinguish them. Moreover this Squirrel, like some Tupaias, lives largely on the ground among fallen logs. Tupaia resembles a Lemur in the complete orbit. The dental formula is I 2/3 C 1/1 Pm 3/3 M 3/3 = 38. The sublingua, too, is stated by Garrod to be like that of Chiromys. There is a minute caecum in T. belangeri, none in T. tana.
Ptilocercus[[371]] has a pen-like posterior portion to the tail, a modification which is found in other groups of animals. The tail of certain Phalangers, for instance, shows this same modification. The rest of the tail is scaly. The animal, as was pointed out by Dr. Gray,[[372]] looks very much like a Phalanger. The orbit is entire as in Tupaia. The fingers and toes are five. The one species, called after Sir Hugh Low, G.C.M.G., P. lowi, is a Bornean animal.
Fam. 3. Centetidae.—This family is entirely confined to the Island of Madagascar. It includes some seven genera. The best-known genus is Centetes. C. ecaudatus, the Tanrec, Tenrec, or Tendrac, is an animal a foot or so in length, without a tail, and with forty-four teeth.[[373]] The immature animal is so different from the parent as to appear quite a different form. It has three narrow rows of spines along the back, which do not wholly disappear until the permanent dentition has been acquired. Even then the hairs are of a rather spiny character, particularly those upon the back of the head, which are erected when the animal is
annoyed. The Tanrec feeds mainly upon earthworms. It is "probably the most prolific of all animals," since as many as twenty-one young are said to have been brought forth at a birth. Some Opossums, however, have twenty-five teats.