On the Characters of the Aye-aye, as a test of the Lamarckian and Darwinis Hypothesis of the Transmutation and Origin of Species. By Professor R OWEN, M.D., F.R.S., F.G.S.

The author, referring to the results of a recent dissection of the Chiromys madegascariensis, Cuv., 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 larvæ 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 det The wide openings of the eyelids, the large cornea and expansile iris, the subglbular 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 disoc 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 woodboring 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 renovation 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 instrument, 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 leave 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-retaining 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 Ayeaye 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 manoeuvre 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

faculties to foresee, invent, and adapt, we dimly conceive, in analogous but more perfect results, the exercise of like faculties in a transcendentally higher degree.

To conceive the direct formation and adjustment of such an organization as that of the Chiromys to its purpose accords best with the mode of our finite human adaptive operations, but least with the sum of present observations bearing upon the origin of species. Such observations have led to the conception that the species of organisms may be due to natural laws or secondary causes, operating to produce them in orderly succession and progression*; and also to the suggestion of the mode of operation of such secondary causest.

As a test of the value of some of these suggestions in making known or rendering intelligible the origin of a species, the organization of the Aye-aye lends itself with peculiar force.

Buffon, assuming that a certain number of species had been originally created after a manner analogous to, and conceivable by, the way in which human machines are made, conceived that there was a tendency in their offspring to degenerate from the original type; and he refers the Linnean species, about 200 in number, which are described in his great work, to about fifteen primitive stocks. As, however, the Aye-aye, had he known as much as is now known of it, might have been referred to a "primitive type or stock," or to one of the "isolated forms" such as Buffon conceived the Elephant and the Mole to be, the author proceeded to apply the Aye-aye, as a test, to Lamarck's hypothesis of the origin of species.

The Philosophie Zoologique' teaches that species, like varieties, have their origin, maturity, and departure, changing with the course of the changing operation of the causes that produced them; that such so-induced changes of form and structure lead to changes in powers and actions, and that such actions become another cause of altered structure; that the more frequent employment of certain parts or organs leads to a proportional increase in the development of such parts; and that as the increased exercise of one part is usually accompanied by a corresponding disuse of another part, this very disuse, by inducing a proportional degree of atrophy, becomes another element in the progressive mutation of organic forms 1. According to the modifying influences suggested by Lamarck, a Lemurine quadruped, attracted by the noise of a boring caterpillar in the bough on which it happened to be perched, instinctively applied its incisors to the bark, and, by frequent repetition of such efforts, increased the mass of the gnawing muscles, which, stimulating the growth of the bone, led to concomitant modifications in the size and proportion of the jaws. The incisors, by repeated pressure, either became welded into a single pair above and below-or, the stimulus to excessive growth being concentrated on one incisor, the neighbouring teeth became atrophied by disuse, and by derivation of their nutrient fluid to the contiguous pulp; hence the preponderating size of the pair of front teeth, and the extent of edentulous space behind them. Concomitantly with the efforts excited by the particular larvivorous tendency of a certain Madagascar Lemur to expose the canal in which its favourite morsel lay hidden, were repeated endeavours to poke the longest finger into the burrow so laid open. The repeated squeezing of the soft skin, with the compression of the nerves and vessels, permanently affected the growth of such digit, and kept it reduced to the blighted state, whereby it happens to be suited to the work of extracting the larva. Lamarck supposes all these changes to be gradual, and effected only through long succession of generations; he assumes that changes of structure, due to habitual efforts and actions, are transmissible to offspring; and he finally invokes, like his successors, the requisite lapse of time and long course of generations. It is to be supposed that, until the modifications of dental and digital structures were brought about, the grub-hunting Lemur subsisted on the necessary proportion of fruits and other food more readily obtainable under the *Owen, 'On the Nature of Limbs,' 8vo, 1849, p. 86.

+ De Maillet, Telliamed, ou Entretiens d'un Philosophe Indien avec un Missionnaire François,' 8vo, 1755. Buffon, Histoire Naturelle, 4to, tom. xiv., “Dégénération des Animaux," p. 311, 1785. Lamarck, Philosophie Zoologique, 8vo, 1809. Vestiges of Creation, 8vo, 1846. Wallace, "On the Tendency of Varieties to depart indefinitely from the Original Type," Proc. Linn. Soc. 1858. Darwin, 'On the Origin of Species,' &c. 8vo, Lamarck, op. cit. tom. i. chap. iii. vi. vii,

1859.

ordinary Lemurine condition. That the same finger should be the seat of the wasting influences on both hands and in all Aye-ayes strikes one as a result hardly to be looked for on the hypothesis of the cause of such specific structures propounded by Lamarck: that there should be a peculiar modification of the muscles of the forearm, whereby both flexor sublimis and flexor profundus combine their action upon the same tendon, pulling the probe-like digit, is left unaccounted for. The physiologist finds still more difficulty in accepting the explanation of the way in which the peculiar size, shape, and law of growth of the incisors could be brought about. The action of muscles pressing upon the bony sockets might affect the growth of teeth filling such sockets, but could not change a tooth of limited growth, like the incisors of an ordinary Lemur, into a tooth of uninterrupted growth. Besides, the crowns of both the scalpriform incisors of the Chiromys and the ordinary small incisors of other Lemurines are formed according to their specific shape and size, before they protrude from the gum: they acquire so much development while the animal still derives its sustenance from the mother's milk. In the Aye-aye the chisel or gouge is prepared prior to the action of the forces by which it is to be worked. The great scalpriform front teeth thus appear to be structures foreordained to be predetermined characters of the grub-extracting Lemur; and one can as little conceive the development of these teeth to be the result of external stimulus or effort, as the development of the tail, or as the atrophy of the digitus medius of both hands. The author had elsewhere tested the Lamarckian hypothesis of transmutation by the phenomena of the dentition of the male Gorilla, and no refutation of his argument had appeared.

There remained then to be seen whether the subsequently propounded hypothesis of "natural selection" would afford a better or more intelligible view of the origin of the species called Chiromys madagascariensis. Applying to the Aye-aye the illustration of his hypothesis, as submitted by Mr. Darwin to the Linnean Society*, it may be admitted that the organization of a Lemur, feeding chiefly on fruits or birds, but sometimes on grubs, is or might become slightly plastic, in the sense of being subject to slight congenital variations of structure. We may also suppose changes to be in progress in the woods of Madagascar causing the number of birds to decrease, and the number of insects to increase, especially of those the larvae of which are xylophagous. The effect of this might be that the Lemur would be driven to try to catch more grubs. His organization being slightly plastic, those individuals with the best hearing, the largest front incisors, and the slenderest middle digit, let the difference be ever so small, would be to that extent favoured, would tend to live longer, and to survive during that time of the year when birds or fruits were scarcest; they would also rear more young, which would tend to inherit these slight peculiarities. Were the Lemurs to be reduced to this insect-food, those individuals less plastic than the incipient Aye-aye, or not verying in the same way, would become extinct. Acceptors of the hypothesis of "natural selection may entertain no more doubt that such causes in a thousand generations would produce a marked effect upon the Lemurine dentition and limbs, adapting the form and structure of the Quadrumane to the catching of wood-boring grubs instead of birds, than that any domesticated quadruped can be improved by selection and careful breeding. But, to the author of the present communication, the propounding of such plastic possibilities left no sense of any knowledge worth holding as to the origin of the species called Chiromys madagascariensis, no help to the conception of such origin which was at all worth so wide a departure from actual experience of facts. He knew of no changes in progress in the Island of Madagascar necessitating a special quest of wood-boring larvæ by small quadrupeds of the Lemurine or Sciurine types of organization. Birds, fruits, and insects abounded there in the ordinary proportions; and the different forms of Lemurida there coexisted, with their several minor modifications, zoologically expressed by the generic terms Lichanotus, Propithecus, Chirogaleus, Lemur, and Chiromys.

On the Zoological Significance of the Cerebral and Pedial Characters of Man. By Professor R. OWEN, M.D., F.R.S., F.G.S.

Professor Owen, in illustration of the above characters, exhibited the casts of * Proceedings, 1858, p. 49.

the brain of a male European and Negro, and a cast of the interior of the cranial cavity of a full-grown male Gorilla; also figures of the bones of the feet of the Man and male Gorilla, in plates from his "Memoir on the Osteology of the Gorilla" (Trans. Zool. Soc. vol. v. pl. 11).

The brain of the Gorilla, as exemplified by such cast, is of a narrow-ovate form, with the small end forward; the cerebrum does not extend beyond the cerebellum; viewed with the lower surface of the medulla oblongata horizontal, it does not extend so far back as the cerebellum does. The difference of size between it and a small-sized Negro's brain was exemplified in the subjoined admeasurements:—

In these admeasurements some deduction from the Gorilla's brain must be made for the thickness of the dura mater and other membranes included in the cast: that of the Negro's brain showed it stript of its membranes; and the admeasurements are from a subject corresponding with the smallest of those figured by Tiedemann in the Philosophical Transactions' for 1836, pl. 32, in which the posterior cerebral lobes extend half an inch beyond the cerebellum.

Although in most cases the Negro's brain is less than that of the European, Tiedemann and the author of the present paper had observed individuals of the Negro race in whom the brain was as large as the average one of the Caucasian; and the author concurred with the great physiologist of Heidelberg in connecting with such cerebral development the fact that there had been no province of intellectual activity in which individuals of the pure Negro race had not distinguished themselves. The contrast between the brains of the Negro and Gorilla, in regard to size, was still greater in respect of the proportional size of the brain to the bodythe weight of a full-grown male Gorilla being one-third more than that of an average-sized Negro.

Passing from this contrast to a comparison of the Gorilla's brain with that of other Quadrumana, the author insisted upon the importance and significance of the much greater difference between the highest ape and lowest man, than existed between any two genera of Quadrumana in this respect; the brain of the Gorilla, in the contraction of the anterior lobes, in the non-development of posterior lobes extending beyond the cerebellum, and in the paucity, symmetry, and relative size of the cerebral convolutions, so far as they were indicated in the cast, closely accorded with the brain of the Chimpanzee. From these to the Lemurs the difference of cerebral development shown in any step of the descensive series was insignificant compared with the great and abrupt rise in cerebral development met with in comparing the brain of the Gorilla with that of the lowest of the human races. This difference paralleled the difference in the structure of the lower limbs, especially the foot, in the Gorilla and Man; on which difference, as exemplified in the Chimpanzee and lower apes and monkeys, Cuvier had founded the ordinal grade to which he had assigned the genus Homo, under the term Bimana. The disposition of the hallux as a hinder thumb, with the concomitant modifications of the tarsal bones, was as strongly marked in the Gorilla as in any lower Quadrumane, and the contrast between the foot-structures of the Gorilla and Negro was as great.

The homologies of the parts in the structure of both brain and foot of the Human and Simial Mammalia being demonstrated, as by Tiedemann and Cuviert, no *Scrobiculus parvus loco cornu posterioris." (Icones Cerebri Simiarum, fol. p. 14, fig. iii. 2.)

"Pouce libre et opposable au lieu du grand orteil." "L'homme est le seul animal vraiment bimane et bipède." (Règne Animal, i. p. 70.) "Pedes hippocampi minores vel ungues, vel calcaria avis, quæ a posteriore corporis callosi tanquam processus duo

hypothesis of the cause of these homologies, with their structural gradations and differences, would abrogate the necessity of the zoological disposition of the different members of the animal kingdom in groups of different degrees of value. The modification of the human foot having been, in the author's opinion, rightly estimated by Cuvier as of ordinal value, he contended that the equal or correlative degree of difference shown in the development of the human brain, regard being had to the higher importance of that organ in the animal frame, necessitated its higher appreciation as a zoological character, and that the now known characters of the Gorilla's brain confirmed the reference of the Bimanous order to the subclass Archencephala.

On the Homologies of the Bones of the Head of the Polypterus niloticus. By Professor R. OWEN, M.D., F.R.S., F.Ĝ.S.

Preparations and sections of the skull of the Polypterus were exhibited, showing the way and proportions in which the bones of the exo- and endo-skeleton were blended together, more especially the extension of the epencephalic segment backward freely beneath the overarching roof of dermal bones, from which the super-, ex-, and par-occipitals were distinct. Professor Owen referred to a paragraph in his Lectures on Comparative Anatomy' (vol. ii. p. 136), in reference to the inconstancy of the dermo-cranial bones of the Sturgeon, and the confusion caused by applying to them the names "super-occipital," "par-occipital," or other synonyms of the vertebral elements of the skull. The same remark applies to Polypterus, Lepidosteus, and many extinct Ganoidei.

On Zoological Provinces. By Sir J. RICHARDSON, F.R.S.

This paper consisted mainly of a single question, "What is a zoological province ?" A right and full answer would, in the author's opinion, open one avenue to the solution of the origin of species which has occupied the naturalists of this country for several years.

He referred to the Palmipede group of birds. The highest latitudes of the Arctic regions to which man has penetrated are the native places of the Snow Goose, and of various other members of the family, who, having reared their young in two brief months, speed to the southward and winter on the verge of the tropics. Is this whole space, little less in extent than a hemisphere, to be accounted a zoological district?

The range of the Whale is not far short; but land-animals have a much less wide distribution. Has every class of the Vertebrata a different zoological province? and how far are any of them conterminous with the provinces marked out by botanists ?

On certain Modifications in the Structures of Diving Animals.

By Prof. ROLLESTON, M.D., F.R.S.

In the class Mammalia, the Cetacea were contrasted with the Phocida, and in the class Aves, the Colymbidæ were contrasted with the Cinclidæ, as to the degree of modification which their tegumentary, circulatory, and osseous systems had undergone in adaptation to their aquatic habits.

The skin of the Seal was less specially modified than that of the Whale, and the aberrations from the ordinary Mammalian character which its bones and teeth presented were in like manner less marked than those of the animals with which it was compared. The teeth in the order Seals were often irregular as regarded their number, their implantation, and their permanence in the jaw; and the epiphyses of the vertebrae were often slow to unite with the bodies. All these particularities were instances of correlation of growth existing between the skin and medullares proficiscuntur, inque fundo cornu posterioris plicas graciles et retroflexas formant, in cerebro Simiarum desunt; nec in cerebro aliorum a me examinatorum mammalium occurrunt; Homini ergo proprii sunt." (Ib. p. 51.) Both the above propositions are susceptible of flat contradiction on homological grounds, and are, nevertheless, true as zoological characters.