EVOLUTION OF MAN SMITH. 561 



fore paws." * They are of "lively disposition and great agility." ^ 

 These vivacious, large-brained little insectivores, linked by mani- 

 fold bonds of relationship to some of the lowliest and most primitive 

 mammals, present in the structure of their skull, teeth, and limbs 

 undoubted (evidence of kinship, remot(> though none the less -sure, 

 with their compatriots the Maylaysian lemui-s, and it is singularly 

 fortunate for us in this inquiry that side by side there should have 

 been preserved from the remote Eocene times, and possibly earlier 

 still, these msectivores, which had almost become primates, and a 

 little primitive lemuroid, the spectral tarsier, which had only just 

 assumed the characters of the primate stock, when nature fixed 

 their types and preserved them throughout the ages, with relatively 

 slight change, for us to study at the present day. 



Thus we are able to mvestigate the influence of an arboreal mode 

 of life in stimulating the progressive development of a primitive 

 mammal and to appreciate precisely what changes were necessary 

 to convert the lively, agile Ptilocercus-like ancestor of the primates 

 into a real primate. 



In the forerunners of the mammalia the cerebral hemisphere was 

 predominantly olfactory in function, and even when the tiiie mam- 

 mal emerged and all the other senses received due representation 

 in the neopallium the animal's behavior was still mfluenced to a 

 much greater extent by smell impressions than by those of the other 

 senses. 



This was due not only to the fact that the sense of smell had 

 already installed its mstruments in and taken firm possession of 

 the cerebral hemisphere long before the advent in this dommant 

 part of the brain of any adequate representation of the other senses, 

 but also, and chiefly, because to a small land-gi-ubbing animal the 

 guidance of smell impressions, whether in the search for food or as 

 a means of recognition of friends or enemies, was much more serv- 

 iceable than all the other senses. Thus the small creature's mental 

 life was lived essentially in an atmosphere of odors, and every object 

 in the outside world was judged primarily and predominantly by 

 its smell. The senses of touch, vision, and hearing were merely 

 auxiliary to the compelling influence of smell. 



Once such a creature left the solid earth and took to an arboreal 

 life all this was changed, foi- away from the ground the guidance 

 of the olfactory sense lost much of its usefulness. Life amidst the 

 branches of trees limits the usefulness of oKactory organs, but it 

 is favorable to the high development of vision, touch, and hearing. 

 Moreover, it demands an agility and quickness of movement that 

 necessitates an efficient motor cortex to control and coordinate 



1 Flower and Lydekker, "Mammals, Living and Extinct," 1891, p. 618. 

 ' W. K. Gregory, op. cit., p. 269, and pp. 279, 280. 



