One word as to the name. Its origin is as stated above, and not from any sound made by the creature itself; for, although one observer states that it sometimes utters a low grunt, another, the Superintendent of the Zoological Gardens in London, says he has never heard it make any sound whatever. Now it could not be expected that scientific naturalists would rest content with so brief a title as Aye Aye for so wonderful an animal. It must have two names at the least—the first to designate its genus, the second to signify the species, just as we say sugar (genus), white or brown, &c., (species); so in 1790 the Aye Aye was called Sciurus (squirrel) Madagascariensis (native of Madagascar). In 1800 it was rechristened as Lemur (ghost) psilodactylus (long-fingered). But it is now generally known by the title bestowed by Cuvier—Chiromys Madagascariensis—which signifies “a rat-like animal with hands, and living in Madagascar.”
The scientific title of the Aye Aye, then, fully atones for the brevity of its common name; and it must be further remembered that the technical names of animals and plants bear no definite relation to their own size or importance; for example, the elephant is simply Elephas Indicus or Africanus, according to the species, while the little changeable mole of the Cape of Good Hope is called Chrysochloris holosericea, and a microscopic rhizopod shell rejoices in the high-sounding title of Quinquenoculina meridionalis. Even this, however, would not be so bad if each species bore but a single name instead of a dozen, as often happens, and if, on the other hand, the same names were not sometimes by mistake applied to totally distinct species. It has been well said that the zeal of zoologists to give names to species and groups is the greatest bane of Natural History, a constant hindrance to our own progress, and a subject of well-deserved reproach from the public; if we would all make it a rule not to publish the name of a supposed new species for a year after its discovery, and until a thorough search had been made for previous records, our own glory might be less apparent, but we should be more considerate of our fellows, and more surely, though more slowly, advance the knowledge of natural objects.
The Aye Aye is about the size of a cat, but the head is rather larger, the ears are wider and less pointed, the limbs project more freely from the trunk, and the bushy tail forms rather more than half the total length of three feet. This tail, moreover, has a gentle downward curve, instead of an upward tendency, as with the cat and the dog. The trunk is clothed with a silky coat of short greyish hair; but the colour is given by the longer hairs, which are dark brown or nearly black, although along the spine some of them are tipped with white.
So far the Aye Aye has presented nothing very wonderful; but a glance at our illustration will detect its most striking feature. The Aye Aye’s hand is unlike that of any other known animal. Its medius or middle digit is about as long as the annularis or ring finger, but only half as thick. It is skinny and bony, as if stricken with palsy, and has been aptly compared to a crooked nail. Its knuckle-joint is projected beyond those of the other digits; its first phalanx is longer than that of any excepting the annularis, and its terminal phalanges very slender. But the tendon of the medius is quite as large as those of the other digits; and we are told that the tendons and muscles are so arranged that great power may be exerted upon this one slender digit, for a purpose we shall presently describe. The pollex, or thumb, is the shortest and thickest of all—has one less phalanx, as is usual among the mammalia, and is armed with a claw like the others. The acute angle which it forms with the palm does not indicate any great degree of opposability.
The hinder foot (pes) reminds us at once of that of a monkey; for the primus, or great toe, stands out boldly from the side of the foot, and is evidently opposed in grasping to the other four dactyls, as is our thumb. It bears a small nail, whereas the four smaller dactyls are armed with curved and pointed claws. Both digits and dactyls, moreover, are a little thickened at the tip, so as to form fleshy pads. That of the primus is most apparent.
The Aye Aye has strange teeth, too; for some of them suggest the squirrel, and others the monkey. In the first place, it has only two front or incisor teeth, above and below, and these are narrow, but deep, and bevelled off to a cutting edge, like the incisor teeth of the beaver, the squirrel, the rabbit, and other “rodentia” or gnawing animals, which have a hard case of enamel upon the front surface, the rest of the tooth being softer and more easily worn away by use. These teeth are like chisels in this respect; but they have two very decided advantages over the best steel instrument of human contrivance. The first is, that their very use keeps them sharp and in perfect order, since the edge of the lower tooth strikes just behind the edge of the upper, and both are continually worn away behind by the attrition of the hard wood which they attack. The second peculiarity is, that this constant loss of substance at the free end of the tooth is constantly repaired by new growth at the opposite extremity. The tooth grows during the life of the animal; and as the crown is worn away, the addition of fresh material to the root pushes the whole tooth slowly forward in its long socket, and it is thus ever ready for use. These ever-growing teeth are organic chisels which are for ever in use, yet never in need of the grindstone—for ever wearing away, yet never worn out.
But while the scalpriform incisors so nearly resemble those of the real rodent mammals, and while this resemblance is further increased by the absence of any canine or eye-teeth, and by the provision for a sliding forward and backward movement of the lower jaw, yet the molar or grinding teeth differ from those of the typical rodents; their crowns are rounded and slightly tuberculous, like those of the pigs, the monkeys, and man, and do not seem adapted to a strictly vegetable diet; add to this the peculiar character of the ears, which are large and naked, like the bat’s, and are inclined forward as if for offensive purposes, rather than backward, like the hare’s, in order to warn it of pursuit, and we must evidently be cautious in drawing conclusions as to the manner of life and the zoological affinities of this singular animal. The limbs show that it climbs trees like a monkey, the eyes that it is active at dusk like the owl and the cat, the teeth that it gnaws wood like the squirrel, while the internal organs of digestion would lead us to suppose that it feeds upon insects; and the extraordinary middle digit is so utterly unlike anything we have seen before, that conjecture as to its purpose seems to be in vain.
Deferring a discussion as to the Aye Aye’s place in a system of animals, and confining ourselves to what we have learned of its structure, let us see how nearly correct the reader has been in any surmises as to its mode of existence by consulting the statements of those who have observed the Aye Aye in life.
The first of these was the traveller Sonnerat, whose Voyage aux Indes Orientales et à la Chine, depuis 1774 jusqu’en 1781, was published at Paris in 1782. He appears to have been the first civilised discoverer of the Aye Aye, and states, either from his own observation or from the reports of the natives, that “it makes use of the long, slender and naked middle digit to draw out of holes in trees the worms which form its food.” Sonnerat had a male and a female Aye Aye which lived for two months on board ship, being fed with rice.
The next recorded observation upon the habits of the Aye Aye was communicated to the French Academy of Sciences in 1855, by M. Liénard, of the Mauritius. He states that when a mango-fruit was offered, the Aye Aye first made a hole in the rind with his strong front teeth, inserted therein his slender middle digit, and then, lowering his mouth to the hole, put into it the pulp which the finger had scooped out of the fruit. A third observer, M. A. Vinson, states that in the same year an Aye Aye drank café au lait or eau sucrée by passing its long and slender digit from the vessel to its mouth with incredible rapidity.