114 REPORT—1862. 
On the Characters of the Aye-aye, as a test of the Lamarckian and Darwinian 
Hypothesis of the Transmutation and Origin of Species. By Professor R. 
Owxn, I.D., F.BRS., F.GS. 
The author, referring to the results of a recent dissection of the Chiromys mada- 
yascariensis, Cuy., said, that most naturalists who had had the opportunity of 
studying the living habits of the Aye-aye in its native climate, from Sonnerat to 
Sandwith, had observed its faculty of detecting larvee boring in wood, of gnawing 
down to their tunnels, and extracting them for food, for which this animal shows 
a predilection; they also describe the animal as sleeping during the heat and glare 
of the tropical day, and moving about chiefly by night. Many particulars of the 
structure of Chiromys closely accord with these alleged habits and natural diet. 
The wide openings of the eyelids, the large cornea and expansile iris, the subglo- 
bular lens and tapetum, were, the author remarked, arrangements for admitting to the 
retina and absorbing the utmost amount of the light which may pervade the forests 
frequented by the Aye-aye at sunset, dawn, or moonlight. Thus the Aye-aye is 
able to guide itself among the branches in quest of its hidden food. To discern 
this, however, another sense had need to be developed to great perfection. The 
large ears are directed to catch and concentrate, and the large acoustic nerve and its 
ministering “ flocculus ” seem designed to appreciate any feeble vibration that might 
reach the tympanum from the recess in the hard timber through which the wood- 
boring larva may be tunnelling its way by repeated scoopings and scrapings of its 
hard mandibles. The Aye-aye was a quadrumanous quadruped, in which the front 
teeth, by their number, size, shape, implantation, and provision for perpetual renova- 
tion of substance, are especially fitted to enable their possessor to gnaw down, with 
gouge-like scoops, to the very spot where the ear indicates the grub to be at work. 
The instincts of the insect, however, warn it to withdraw from the part of the 
burrow that may be thus exposed. Had the Aye-aye possessed no other instru- 
ment, were no other part of its frame specially modified to meet this exigency, 
it must have proceeded to apply the incisive chisels in order to lay bare the whole 
of the larval tunnel, to the extent at least which would leaye no further room for 
the retracted grub’s retreat. Such labour would, however, be too much for the 
reproductive power of even its strong-built, wide-based, deep-planted, pulp-retain- 
ing incisors ; in most instances we may well conceive such labour of exposure to be 
disproportionate to the morsel so obtained. Another part of the frame of the Aye- 
aye is, accordingly, modified in a singular and, as it seems, anomalous way, to 
meet this exigency. We may suppose that the larva retracts its head so far from 
the opening gnawed into its burrow as to be out of reach of the lips, teeth, or 
tongue of the Aye-aye. One finger, however, the medius, on each hand of that 
animal has been ordained to grow in length, but not in thickness, with the other 
digits ; it remains slender as a probe, and is provided at the end with a tactile pad 
and a hook-like claw. By the doubtless rapid insertion and delicate application of 
this digit, the grub is felt, seized, and drawn out. For this delicate manceuvre the 
Aye-aye needs a free command of its upper or fore limbs; and to give it that power, 
one of the digits of the hind foot is so modified and directed that it can be applied, 
thumb-wise, to the other toes, and the foot is made a prehensile hand. Hereby the 
body is steadied by the firm grasp of these hinder hands during all the operations of 
the head, jaws, teeth, and fore paws, required for the discovery and capture of the 
common and favourite food of the nocturnal animal. 
Thus we have not only obvious, direct, and perfect adaptations of particular 
mechanical instruments to particular functions—of feet to grasp, of teeth to erode, 
of a digit to feel and to extract,—but we discern a correlation of these several 
modifications with each other, and with modifications of the nervous system and 
sense-organs—of eyes to catch the least glimmer of light, and of ears to detect the 
feeblest grating of sound,—the whole determining a compound mechanism to the 
perfect performance of a particular kind of work. 
But all this must have a cause; and we are led to a conception of the nature of 
such cause by the analogy of its effect with that of the exercise of faculties that 
energize in our own intellectual nature—ours, too, the highest that we have direct 
and material cognizance of in this sphere of life and labour—in which, with such 
