The Lemuroida as a group have some general characters in common. Firstly, they are all Quadrumanous, and the hinder thumbs are in most very large, strong, opposable to the other digits, and capable of much movement. Furnished also with well-made thumbs on the hands, they have a great power of grasp, and of clasping boughs and large creeping plants during their active climbing and jumping. Then there are special structures on the tips of the fingers; these are flattening of the tips into disc-or button-shaped pads, on the upper surface of which is the nail. The skin of these rounded tips covers a cushion of fat, and is well supplied with sensitive nerves, and hence they are not only cushions, but extremely fine points of touch. Their use is evidently connected with the extremely agile boundings, from branch to branch, during the hours when there is little or no light. The sense of feeling, then, replaces that of sight to a great extent, and the supply of nerves is sufficient to excite the muscles of the fingers and hands, toes and feet, to hold on at the least touch; while the cushions of fat prevent the extremities from being jarred. These curious tips give a very clumsy appearance to the digits, even when they are extremely small. There is a true claw on the second digit (toe) of the foot, and nails on the other fingers and toes in some Lemuroids, but there are different arrangements of the claws in others. It is noticed when several kinds of them are examined, that there is a great difference in their digits as regards their size and length, and the fourth is the longest instead of the third, as in man: but sometimes the index, or first finger, not counting the thumb, is much reduced in size, and in two forms it is very defective, and only a little knob remains to show its position; but this apparent deformity has something to do with their method of life. The thumbs are well formed, and so are the third, fourth, and fifth digits, the index being as just mentioned, and the result is to divide the hands, as it were, into two opposing portions, giving a grasp like that of the climbing birds—the Parrot, for instance. These kinds of Lemuroida creep slowly towards their prey, and clasp the branches firmly before they jump on the insect they desire to catch. Besides these peculiarities of the hands and feet, which, moreover, are supplied in every joint with tendons and muscles of great motive power, the fore-arm is capable of turning the wrist forwards or backwards, or, as it is called, rotating, and also of bending. Again, the upper arm is loosely but firmly attached to the shoulders and neck, so as to admit of great range of motion, so what with the bending and rotation of the fore-arm, and the mobility and cushioned state of the fingers, these creatures possess a wonderful apparatus, suited for extreme action and safe holding on. The ability to rest on the hind legs and jump like a Kangaroo (see [page 5]), which is peculiar to some kinds, depends also upon peculiar structures. The ankle-bones are very long in these, so long, indeed, as to make the foot resemble that of a Frog when jumping more than that of any other animal. The long ankle-bone acts as part of a lever, and enables the muscles of the back of the leg to act on the foot so as to project the creature high in the air, or for many feet from one bough to another, or along the ground. There is nothing like this in the Monkeys. Now, the woolly fur of the Lemuroids, and their cylindrical woolly tails, at first sight appear to be encumbrances to an active animal which lives in the tropics, but they are all extremely chilly creatures, and love heat; moreover, it is possible that severe falls may be rendered less injurious by the deadening influence of a soft fur. The tail is a wonderful apparatus in some kinds, and barely exists in others, being, however, never prehensile even when longest and strongest. Probably it is used as a kind of adjuster of movements in rapid exercise, and certainly it is a great comfort to many, for several kinds like to curl it over their backs, or round their necks, like a sable boa, whilst they are asleep, or basking in the sun. In one kind it is supplied with a marvellous set of tendons, and, indeed, to such an extent of complexity, that it would appear that Nature had lavished mechanical appliances to every joint without any very definite use. It is remarkable that in those Lemuroida which have no tail, or barely a trace, there is a curious arrangement of the blood-vessels. The limbs in these kinds are not supplied with main arteries, and veins with long branches, but the blood-vessels form a closely-packed set of tubes of very small size. This network, in the language of science, is called a rete mirabile, “a wonderful network,” for such it is. Curiously enough this arrangement of the blood-vessels is found in some totally different animals, whose movements are very slow and cautious, such as the Sloths, for instance. Equally slow are the movements of some of the kinds of Lemuroida which possess this interesting structure. It has been suggested that this novel division and subdivision of the blood-vessels tends to produce slowness of movement, and it may be said in a general way that the active Lemuroida and active animals of other orders do not have a rete mirabile.
EYE OF LEMUROID,
SHOWING CONTRACTION
AND DILATATION OF PUPIL.
(Original, after Murie.)
Some Lemuroids have short, and others have long muzzles, and there is great variety in the shape of the head. Evidently those with long noses have a very fine sense of smelling, and the whole of the members of the sub-order have a peculiar twist in the outside nostril, which distinguishes them from the Monkeys of both the Old and the New World. This twist was thought to be of great importance in classifying the Lemuroida in the animal scale, and they are often at the present day termed “Strepsirhini,” from the Greek words which mean curved nostril. Some scent out insects and grubs under the bark of trees, and all use this sense in searching for food by night. There are some long hairs about the upper lip and cheeks like those of a Cat, and these “smellers” are doubtless extremely sensitive to touch, and although they do not assist the sense of smelling, they help the animals in avoiding danger in their movements through the dark underwood.
The colour of the iris (the membrane around the pupil of the eyes) is very beautiful in most, and as the eye is large and staring, it is well seen. Sometimes the pupil is round, but in some kinds it is a slit, as it is in the domestic Cat, for instance, and this shape has much to do with their nocturnal habits. The iris moves in two directions, and makes the pupil either larger or smaller; and the importance of this gift is, that whilst a small pupil admits only a very slight quantity of light into the body of the eye, a large one allows a great amount to enter; hence, at eventide the pupil dilates, or, in other words, the iris acts so as to enlarge it, and all the light possible enters, but in sunlight the pupil contracts, even to a point, the iris moving so as to shut out the superfluous and injurious illumination. The nocturnal kinds require a very dilatable pupil, for they move often in comparative darkness, and when the least ray of light is of benefit to them. Besides this structure, there is another which has to do with husbanding, and making the most of faint light. If the eyes of a Lemur are examined a little carefully, they will be found to glare with a very metallic lustre in certain lights, just as those of a Dog and Cat. It appears that in certain animals, and in the Lemuroids, there is a peculiar layer within the eye which looks coloured; but really it is only very finely marked by fibres, which decompose the common white light into its primitive colours, in the same manner as the extremely delicate markings invisible to the naked eye on mother-of-pearl produce the well-known beautifully iridescent tints. This layer is behind the sensitive layer of the eye, and it acts as a concave reflector, collecting the slightest glimmers, and making them of use. The membrane is called the tapetum. It has been noticed that there is a difference in the expression of the eyes of the Lemuroids and Monkeys, and certainly these last have the advantage of showing their impudence, malice, and fear in their beautiful organs of sight.
The ears of some Lemuroida are small, but in the majority not only are they large, but they possess singular powers of movement, and in some can be folded up. The sense of hearing is undoubtedly acute in the nocturnal kinds, and their capacious ears are of immense importance to them, for they have to discover their prey by their sense of smell and sight, and also to be on the alert against their natural enemies.
UPPER SURFACE BRAIN
OF LEMUR CATTA.
(Original, after Murie.)
There is a singular want of sameness in the teeth of the Lemuroida, and several kinds, which apparently lead the same sort of lives, and eat the same food, have different arrangements of the cutting and grinding teeth. Sometimes the front teeth fall out when the second set is cut, and are not replaced, and in the Aye-Aye they act as perfect chisels. As a rule, in all kinds, the lower front teeth project horizontally forwards from the jaw, and somewhat resemble in their direction those of the Marmosets, but the upper ones are straight. As the Lemuroida live easily and perform movements of very much the same character year after year, their brains are not much called upon. They are not as tractable or as intelligent as Monkeys, and although their muscles act with vigour and ease, still they are not required to perform the actions which are regulated by the superior intelligence of the Apes. Hence it is not to be expected that the brain of the Lemuroida will be as well developed as that of the Ape or Monkey. It is, in reality, not so bulky, and not so convoluted. The brain is low in height, longer than broad, and does not cover the cerebellum. Finally, the young Lemuroida are nourished within their parent through a placenta, which is diffuse, and more or less disc-shaped, and therefore unlike that of the animals already described, and of man.
They have a peculiarity about the under part of the tongue, namely, beneath its tip there is a fringe of scaly flesh, the free ends of which, when the mouth is shut, fit in between the front teeth. Its use is unknown, but some have said that it is to keep the back of the teeth and the spaces between them clean.