116 REPORT—1862. 
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, 1s 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. Be- 
sides, 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 fore- 
ordained—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 illus- 
tration 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 larva 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 varying 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 propound- 
ing 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 necessi- 
tating a special quest of wood-boring larvee 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 Lemuride 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. Owrn, W.D., F.BS., EGS. 
Professor Owen, in illustration of the above characters, exhibited the casts of 
* Proceedings, 1858, p. 49. 
