CHAP. IV] THE GENERAL ANATOMY OF THE CERCOPITHECIDAE 121 



Unlike the nocturnal Lemurs, the Cercopitheci move abroad 

 in daylight, and such a change in habits surely provides a sug- 

 gestion as to the possibilities of evolutionary progress. 



Almost as impressive as the development of the apparatus of 

 vision, is the reduction of the organ representative of the sense 

 of smell, and it is probable that that of hearing has also degenerated 

 to some extent. By way of compensation, some refinement of the 

 tactile sense is inferred from the conformation of certain parts of 

 the skin. Finally the brain is relatively large in size, and if a 

 balance be struck between the gains and losses experienced by 

 the various organs of sensation outlined above, the brain-mass 

 may appear unduly great. The clue to this difficulty will be 

 found in a study of the so-called "association areas" of the cerebral 

 surface. These also have increased in extent. Such an increase 

 is indicative of the advancing development of the faculty of asso- 

 ciating sense impressions, of powers which through evolution 

 culminate in an intellect of human type. Yet the Cercopitheci 

 are far from having attained that stage, and while the variability 

 of these animals may be remarked once more, it is also to be 

 remembered that if we judge of their behaviour and mode of life 

 from the standpoint of the ordinary observer, we must admit that 

 many of them do not seem to have advanced far beyond the 

 Lemurs. 



In the following paragraphs the detailed descriptions are based 

 mainly upon the conditions noted in specimens of the genus 

 Cercopithecus. But in some instances (which will be indicated) 

 recourse has been had to more accessible material, viz. examples 

 of the genera Macacus, Cynocephalus and Semnopithecus. The 

 Cercopitheci are characteristically African in their geographical 

 distribution, while the genus Macacus is typically Asiatic. The 

 Cynocephalous apes are encountered in Arabia and Abyssinia, 

 i.e. in an intermediate area, but since they are distributed through 

 the length and breadth of Africa, their relations are with that 

 continent rather than with Asia. 



A. General External Characters. The species of the genus 

 Cercopithecus amount in number to about forty, and consequently 

 the description of their external characters, if brief, must be of a 

 general nature only. 



