94 PROFESSOR OWEN ON THE AYE-AYE. 



like digit, is left unaccounted for. The physiologist finds still more difficulty in 

 accepting the explanation of the way in which the peculiar conditions 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 fore-ordained — to be pre- 

 determined 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 develop- 

 ment of the tail, or as the atrophy of the digitus medius of both hands. I have, on a 

 former occasion, tested the Lamarckian hypothesis of transmutation by the phenomena 

 of the dentition of the male Gorilla', and have not yet seen a refutation of my argument. 

 A strong superorbital ridge may project, as an occasional variety, in Man ; and may be 

 supposed to exemplify the way in which, on the degeneration-hypothesis, Man might 

 sink into the Ape. But such a fact in no way affects the physiological conclusions 

 against the Lamarckian doctrine of transmutation. 



There remains, then, to be seen whether the subsequently propounded hypothesis of 

 ' natural selection ' will afford us a better or more intelligible view of the origin of the 

 species called Chiromys madagascariensis. 



I may remark, on the outset, that this hypothesis differs from Lamarck's in invoking 

 a supernatural commencement of organisms which are held to have been "descended 

 from some one primordial form, into which life was first breathed "'-. And herein is 

 one main distinction between it and the ' derivative hypothesis,' which maintains that 

 single-celled organisms, so diversified as to be relegated to distinct orders and classes 

 of Protozoa, are now, as heretofore, in course of creation, or formation, by the ordained 

 potentiality of second causes ; with innate capacities of variation and development, 

 giving rise, in long course of generations, to such differentiated beings as may be 

 distinguished by the terms ' plant ' and ' animal ;' from which all higher animals and 

 plants have, through like influences, ascended, and are being ascensively derived. 

 This, as the naturalist knows, is mere hypothesis, at present destitute of proof. But 

 it is more consistent with the phenomena of life about us, with the ever-recurring 

 appearance of mould and monads, and with the coexistence, at the present time, of all 

 grades of life rising therefrom up to Man, than is the notion of the origin of life which 

 is propounded in Mr. Darwin's book ' On the Origin of Species by Natural Selection.' 



' Trans. Zool. Soc. toI. iii. p. 381, and toI. iv. p. 1/5. See also 'Classification of the Mammalia,' 8to, 

 1859, p. 101. " Darwin, 'On the Origin of Species,' p. 414. 



