96 PROFESSOR OWEN ON THE AYE-AYE. 



species. Every new instance of structures which do not obviously, and without straining, 

 receive a teleological explanation, especially the great series of anatomical facts expressed 

 by the " law of vegetative or irrelative repetition," — all congenital varieties, deformities, 

 monstrosities, — oppose themselves to the hypothesis of the origin of a species by a 

 primary or immediate and never-repeated act of adaptive construction. 



Such series of facts, with those treated of in my works ' On the Homologies of the 

 Vertebrate Skeleton' and ' On the Nature of Limbs,' appear to me to be the chief 

 grounds in zoological science for the hypothesis of a continuously operative secondary 

 creational law. That this law works by derivation of one species from a previous 

 species, of a new from an old species, is made probable by the demonstrated unity of 

 plan in the Articulate and Vertebrate types of organization, and by the approximations 

 to such unity of type in the molluscous and some lower forms of organized beings. 

 The phenomena of parthenogenesis have made known unexpected and strange instances 

 of great degrees of difference of form between the self-subsistent independent gene- 

 rative product and the producing organism. But the "derivative hypothesis" is, at 

 present, as I have already admitted, little more than an indication of a route of 

 research by which the mode and way of derivation may be ultimately better understood. 

 The terms in which the zoologist would express the sum of the observations above 



recorded on the Aye-aye would be, " that it was related by affinity to the Quadrumana, 



and by analogy to the Rodentia." 



And such terms become intelligible if they mean that the Aye-aye has been derived, in 



common with other existing Lemurida, from some pre-existent animal of a more 



generalized Lemurine type of organization, in departing from which it has gained a 



character, e.g. the dental one, very like that which prevails in the Rodentia, without losing 



the more numerous and essential characters of its inherited Lemurine organization. 

 The terms in which the anatomist would express the sum of his observations on the 



structural resemblances traceable from the Aye-aye throughout the Lemuridce would be, 



that the principle of ' unity of organization ' prevailed through such group. 



And such term would have a more intelligible meaning on the hypothesis that these 



singularly diversified Lemurs were genetically related by descent from a common 



ancestral form. 



Whilst admitting the general evidence, therefore, in favour of ' creation by law,' I am 



compelled to acknowledge ignorance of how such secondary causes may have operated 



in the origin of the Chiromys. Darwin seems to be as far from giving a satisfactory 



explanation of them as Lamarck. 



One discerns in the Lemuridas, if we therein include the Galeopitheci, such a range of 



variety in their dentition as suggests the idea of instability of character, or of unusual 



plasticity, in that part of their organization. 



The varieties of the limbs, also, as manifested by the long ankle-bones of Otolicnus 



and Tarsius, by the reduction of the index to a stump in Perodicticus, and by the atrophy 



