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Show 508 MR. ST. G. MIVART ON THE LEMURS. [May 20, difference, it should be remembered that amongst Apes we find in Ateles an extraordinary elongation of that organ, while no naturalist would think of separating from the orders Insectivora and Rodentia such forms as Talpa, Arvicola, Lagostomus, and Bathyergus because in them this structure is, as in the Lemuroids, perforated by the urethra. Nevertheless whatever objections may be made to the above distinctive characters taken one by one, it is not, I think, to be contested that, taken together, they render it in the highest degree improbable that the Lemuroids and Apes took origin from any common root-form not equally a progenitor of other Mammalian orders. Consequently, if genetic affinity is to be our standard, the Lemuroidea should rank as a distinct order. Considerations, however, have been already advanced against the adoption of such a standard ; and yet other reasons will, I think, become obvious from a consideration of minor groups. As to the second question then, namely the value of the characters which define subordinate groups, it may be well to compare together the Simiadae and Cebidae. If the difference as to the development of the pollex in Lemuroids and Apes is of weight, w h y is not as much weight to be attached to the entirely different character of that organ in the two great groups of Apes ? If the dental distinctions between Lemuroids and Apes are to be considered to tell against genetic affinity, w h y should not the combined diminution of molars and augmentation of premolars so tell also in Hapale ? If an oblique ridge on the grinding-teeth can arise independently in Galago and Ateles, why may it not arise independently in Ateles and Simia ? If the absence in one case of a postorbital extension of the alisphenoid and malar counts against the common origin of Lemur and Cynocephalus, why should not the absence of a bony meatus auditorius externus in Mycetes also count against its affinity to Cynocephalus also ? If the greater relative size of the anterior hyoidean cornua is a bar to the assignment of a common origin between Galago and Colobus, why should not the presence of a jointed anterior cornu in Lagothrix form a bar to the assignment of a common origin to that A p e and to Colobus ? I must confess that I find it exceedingly difficult to conceive that the universal presence of a long bony meatus auditorius externus in the Simiadae and its equally universal absence in the Cebidae can be accounted for any exigences of the struggle for life upon incipient or primordial Ape-forms. To this character must be added the many others which divide the Apes of the two hemispheres, namely :-(1) their different dentition ; (2) the broad nasal septum of the New-World Apes; (3) the tendency of the Cebidce to a curled tail-end, and the constant absence of any manifestation of such a tendency in the Simiadae; (4) the |