But there is a curious arrangement of the fingers, for the index finger of the hand (that is to say, the first finger, not counting the thumb) is shorter than the fifth, so that their “fore finger” is a little finger. The toe-thumb is placed widely from the toes, and rather backwardly, and the toes are united together by a kind of fold or web of the skin which reaches up to the first joint; moreover, the first toe (not including the toe-thumb) has a curved claw on it. They are not good walkers, any more than the Apes, although, like them, they assume the erect position, and it is only on very rare occasions, and when it is necessary to cross a tract of land to get to trees with more fruit upon them, that they attempt to put the foot to the ground. It is not their natural position, and they seem to be quite out of their element. When they come to the ground they rest on the outer edges of the feet, and soon drop on their hands, on the corresponding parts of which they support themselves. So walking is performed with difficulty, and not with grace, and in this they may be compared with the Orangs; but in the Indris the arms are always shorter than the legs. In the trees and branches, which are their favourite haunts, they climb easily, rapidly, and with grace, running along the boughs, jumping to great distances, and alighting with unerring certainty, and clinging on with wonderful tenacity. The structure of the muscles, bones, and ligaments enables them to lead this active arboreal existence, and so strong is their power of grasp, that it remains sometimes after death, for it has happened that in shooting them whilst clinging to the branches they have remained suspended after having been mortally wounded, or dead.
Being dwellers in the foliage of the trees, and amongst the network of branches, twigs, and creepers, the kinds of Indris have a choice of many kinds of food. Leaves, buds, fruit, insects, eggs, and small birds are constantly within their reach, but usually they do not hunt or chase prey, and are satisfied with the best fruit they can find, and other vegetable substances. Nevertheless, they do not despise or reject a bird as something out of the common way of diet, and they open the skull and suck the brains. The teeth are not very well suited for stopping and killing living prey, for in the grown-up individuals there are no lower canines, there being only an upper pair, and thus one of the most important seizing and killing arrangements is absent. On the other hand there are plenty of crushing teeth, with sharp points to them, which enable the Indris to champ fruit without much side to side movement of the jaw being permitted. There are two false, or premolars on each side in both jaws, and three molar teeth behind them. Besides these there are four front teeth in both jaws. In all there are thirty teeth, a smaller number than in any of the animals yet considered.
The upper front teeth, or incisors (four in number only), project forwards very slightly, and nearly bite up and down; but the four lower front teeth (incisors) project well forwards, and the outer pair of them are sometimes called canines, but their office is plainly the same as that of the other front teeth. The predominance of the crushing teeth (there being twenty of them) over those adapted for tearing flesh, denotes that these animals should have a vegetable diet, and this requires larger digestive organs, as the food is bulky. So it is found that the stomach is single, and then there is a very large cæcum, or blind-gut, which ends in a large intestine, which is very long, and twisted on itself, so as to form two regular folds, one on the other, instead of one, as is commonly observed in the higher animals already noticed; in fact, the arrangement is not very unlike that of the sheep, whilst the cæcum is on the same scale as that of that great vegetarian, the Rabbit. These large parts of the digestive apparatus are common to most vegetable-eating animals, whilst the flesh-eaters have them short and small.
But the Indris does not begin life with the prospect of being a vegetarian, for it has a first set of teeth, or milk teeth, as they are termed, and these are shed to make way for the second, or permanent set. Now, it is most curious that the young should have more teeth than the elders, and that were this first set to persist through life, it would indicate a very mixed-feeding animal. The little ones have no less than thirty-four teeth, and they have two lower canines, and two extra lower false molars more than the adults. As age increases all these first teeth gradually fall out, and are replaced, to a certain extent, by the second set mentioned above.
SKULL OF BLACK INDRIS, SHOWING
ADULT DENTITION.
MILK DENTITION OF INDRIS. c, CANINE, AND
p, PREMOLAR, NOT REPLACED IN ADULT.
Now, what is the meaning of this? Why should the young have a larger set than the adults? Clearly those of the adult are admirably adapted for its life, and it is equally evident that those of the young are of no particular use to them. They are either suckling, or are eating fruits obtained for them, and do not kill and feed on birds and living things. It is found that the milk teeth of Indris correspond with the adult or permanent set of such an animal as the Ring-tailed Lemur, which belongs to a different genus. Hence the perfect condition of the teeth of the genus Lemur are the same as the first arrangement of the teeth in the genus Indris. It tends to prove that there is some genealogical relationship between the two genera, and that they were derived from a common ancestor. Moreover, it may be assumed that the milk teeth of all animals are inherited from a perfect and adult ancestral form which was less highly organised or constituted.
It is said that the female Indris has but one little one at a time, and that they are all gentle and timid, being rarely kept for any time in captivity. They are nocturnal in their habits, and evidently have extremely sensitive vision, and, like the others which lead this life, they are protected from many jarring falls by the structure of their hands and feet.