470 ON THE ZOOLOGICAL POSITION 



Comparing lii/cticebus and Plihecia as representatives of the 

 Lemuroidea and Oebidaj of ;ipproximately the same size (each 

 weighing about 500 grm.), it is found that the brain of the 

 former varies in weight from 7*72 to 8" 18 grm., whei-eas the 

 monkey's brain ranges from 22 to 36"2 grm. In other words, 

 the lowly Platyrrhine has from three to four times as big a 

 brain as the Lemuroid. To one who studies the meaning of the 

 size of the cerebral cortex in the different mammalian Orders, 

 and realises the significant role such expansion of the brain has 

 played, ever since Eocene times, in the evolution of the higher 

 mammals, and especially of tlie Primates, it will be evident that 

 a vast chasm sepai-ates the monkeys from the Lemurs. Now 

 Engen Dubois states * that the proportion of brain to body in 

 Tarsius is not appreciably difierent from that of jVi/cticebtcs. In 

 other words, judged by this fundainental test, Tarsias is sharply 

 differentiated from the Apes and occupies a rank not unlike that 

 of a Lemur. As Cope pointed out more than thirty years ago, the 

 brain of Tarsius is not appreciably bigger than that of the Eocene 

 Anaptomor2:)h'as f. 



The ancestors of Tarsius, in fact, fell out of the race for 

 intellectual supremacy in Early Eocene times and ceased 

 cultivating their cerebral organs. Eventually, like the Lemurs, 

 tliey had to adopt nocturnal habits to avoid the risk of extinc- 

 tion. At the same time another branch of the Tarsioids was 

 cultivating more highly skilled movements, and acquiring greatly 

 enhanced powei-s of discrimination and ability to profit from 

 experience. In course of time — and probably long before the 

 close of the Eocene — this particular family of big-brained 

 • Tarsioids was transformed into real monkeys and became the 

 ancestors of the Anthropoidea, 



Before leaving this aspect of the problem, and while emphasising 

 the fact that so far as size of brain is concerned Tarsias is on the 

 same level as the Lemuroids, it is important to remember that at 

 the commencement of the Eocene period the representatives of 

 both the Lemuroidea and the Tarsioidea (and no doubt their 

 common Prosimian ancestors) were equally distinguished from 

 all other Orders by their relatively large brain. Both, in fact, 

 shared alike in the fiuidamental structui-al change that brought 

 the Primates into being. Even the modern Lemuroids, poorly 

 equipped as they are in brain-substance as compared with the 

 Apes, are better ofi' in this respect than members of similar size 

 of any other Order. Thus in the Carnivora,, which come next to 

 the Primates in respect of size of brain, it is found that in 



* ' Proceedings of the Pouvtli International Congress of Zoology,' Cambridge, 1898, 

 p. 91. 



t E. B. Cope, " The Lemuroidea and the Ins9ctivora of the Eocene Period of 

 North America," American Naturalist, Ma.y 1885, p. 467. 



Discussing the size of the cranial cavity of AnapiotimrpJins, he wrote : — "The 

 brain and its hemispheres are uot at all smaller than those of Tarsius. . . . This is 

 important in view of the very small brains of the Hesh-eating and ungulate Mammalia 

 of the Eocene period as yet known. In conclusion, there is no doubt but tliat the 

 genus Anaptomorplius is the most Simian lenmr yet discovered, and jjrobably repre- 

 sents the family from which the anthropoid monkeys and men were derived." 



