VARIETIES IN EPIDERMIS 151 



practises ca' canny, as we know to our cost when we go out in the 

 morning and find great heaps of soft earth thrown up in the line 

 of its advance from its base or fortress. Such a mode of life lends 

 itself remarkably to the kind of skin on its feet, and this is now at 

 any rate adapted to its environment. 



The capybara is a large, heavily-built rodent, and has rather 

 a smooth epidermis not specially thick, with long and efficient 

 papillse of the corium shown in microscopical sections. Being 

 largely aquatic in its habitat, and given to frequenting marshy 

 ground and to enjoying as much sleep as it can manage, it depends 

 a good deal for discrimination of objects on its sensitive corium, 

 and its epidermis is not much specialised for, or by friction and 

 pressure in walking. It does not acquire by reason of stimuli and 

 response any unnecessary tools. 



With this may be classed the echidna or Australian ant-eater 

 which has sparse hairs set on a hard and slightly corrugated epider- 

 mis, and, being mainly a nocturnal animal and living a secluded 

 life, it does not walk much or far in its stealthy pursuit of worms 

 and insects, and the stimuli of friction or pressure encountered 

 by it are few. 



A similar condition is found on the feet of many small carni- 

 vores. 



Animals with scales on their feet, which are held to constitute 

 the earliest stage of the Primate modification of papillary ridges 

 are such as the potoroo, wallaby, kangaroo and giant ant-eater. Such 

 scales register a long, long series of stimuli of friction and pressure 

 in these and their ancestors, in a level of life before any delicate 

 discrimination of surfaces came into operation. 



The nodular form of skin is present in the Canadian tree porcu- 

 pine, where rough nodules cluster closely on the surface of both 

 feet, and it is a significant fact that it shares with the American 

 opossum the peculiarity of nodules on the ventral surface of the 

 powerful prehensile tail. This adaptation tends to efficiency in its 

 arboreal life, and may well have been produced by infinitely small 

 degrees of response in structure in the course of a long evolution. 



The rabbit alone ha\e I found with rod -like projections of the 

 epidermic cells, among which are set in dense order the soft, long, 

 delicate hairs and which thus conduce to its wonderful power of 

 treading on sharp objects without injury. We thus see the inner 

 meaning of dear old Brer Rabbit's jeer of triumph to Brer Fox, 

 " Born and bred in a brier bush." This adaptation might be an 

 unit-character segregated from the ancestral stock of the Leporidae, 

 or it might not, but at any rate the rabbit leads a life in which its 



