154 ARBOREAL MAN 



lost much of its usefulness; and in the case of aquatic 

 Mammals, the whole smell apparatus atrophied, and in 

 some cases vanished. We need not stop to consider the 

 aquatic Mammal, because a life in the water calls for such 

 marked specialization of structure that such creatures 

 disaj)pear from the race for mammalian supremacy. But 

 the case is very different with arboreal Mammals. Life 

 amidst the branches limits the usefulness of the olfactory 

 organs." 



So much seems evident; the only difficulty is for us, 

 with our manifold channels of information, to realize how 

 thoroughly the lowly terrestrial Vertebrates live their 

 whole lives dominated by dependence upon the sense 

 of smell. Friends, and food, are found by their scent, 

 foes are avoided by the same sense, and the whole sexual 

 life of the animal is lived in a like atmosphere. This is 

 very largely the case even with the lowest Eutherian 

 Mammals, and perhaps as familiar an example of the 

 scent-dominated Mammal as can be chosen is the common 

 English Shrew (Sorex araneus). In one feature this 

 inquiry may be removed from the realms of the psychical 

 into the domain of gross anatomy, and that altogether 

 apart from a study of the structure of the brain. Scent 

 glands of various kinds are most important anatomical 

 features of these small and primitive Insectivora, and in 

 them they reach a bewildering degree of complexity of 

 development; but scent glands diminish steadily in those 

 stocks which are truly arboreal. No trail of scent is 

 laid among the branches of a tree, and for an animal that 

 bas become truly arboreal these glands are comparatively 

 useless structures. In the tree-haunting Insectivora 

 they have diminished, the anal glands being their last 

 survivals. " In Chiromys and some other Lemuridae the 

 anal glands are reduced to two shallow cutaneous pits 

 at the sides and upper part of the vent: in the higher 

 ■Quadrumana this trace disappears " (Owen). 



In the olfactory parts of the brain, and in the sensory 



