NERVOUS SYSTEM. VERTEBRATA. 3d 



specialised as the brain is in both families, that of the Aye- 

 aye clearly exhibits features indicative of the affinity of its 

 possessor to the Lemurs. At the same time several of the 

 peculiarities of the brain of Daulentonia are unquestionably 

 features intermediate between those of the great body of 

 mammals and the Primates (more especially the Lemurs), 

 and as such afford the clue to the interpretation of an exact 

 comparison between the Primates and other mammals, 

 which would otherwise be far less definite and sure than it 

 is now possible to make it *. 



The accounts of the Aye-aye's brain which have hitherto 

 been published by Owen, Oudemans, and Chud/insky, and 

 Gervais's remarks concerning a cast of the cranial cavity, 

 are so conflicting that one would hardly imagine that 

 they all apply to the same species of mammal. Moreover 

 they all seem to me to disregard the most instructive and 

 significant features of this remarkable brain. It must, 

 however, be admitted that the brain is subject to extreme 

 variation in this species a fact which emphasises the 

 importance of those features which are constant ; and 

 fortunately the two specimens in this Collection are not 

 unlike the only two examples of which we possess anything 

 like an intelligible account. Specimen D. 531 might be 

 compared with that described by Oudemans, and D. 532 

 with that described by Owen f. 



The cerebral hemispheres completely overlap the broad, 

 flattened olfactory bulbs, but in the caudal direction they 

 are so short as to leave almost the whole of the cerebellum 

 uncovered. In the latter respect they approximate to the 

 condition found in the Carnivora and Ungulata more de- 

 cidedly than do the Lemur's cerebral hemispheres. 



* The fact that many of these peculiarities are undoubtedly due to retro- 

 gressive changes does not, in this particular instance, lessen their importance. 



f I was at first inclined to believe that this old specimen, which 1 found 

 only after searching through the Store-room of this Museum, had probably 

 been stowed away there since the late Sir Richard Owen was Conservator, 

 and might be the identical specimen described by him in the ' Transactions ' 

 of the Zoological Society. But he described and figured a dissection of his 

 specimen, whereas this was undissected when I happened to find it. There 

 was no note, either with the specimen or in the old manuscript catalogue, 

 to indicate the source of this interesting brain. 



