A SQUIRREL'S NEST. 93 



stupid marsupials, the opossum has a true thumb to his 

 hind foot, which he uses like a hand, besides possessing 

 a very flexible tail ; and the opossum is not only pro- 

 verbially cunning, but he also has alone succeeded in 

 holding his own among the highly developed mammals of 

 America, while all the rest of his kind are now confined 

 to Australia, their compeers elsewhere having been killed 

 out without exception during the tertiary period by the 

 fierce competition of the larger continents. Wherever 

 we find a clever animal, like the dog, without any grasp- 

 ing power, we also find a large development of the sense 

 of smell, which may be regarded as to some extent com- 

 pensatory. But it must never be forgotten that the 

 cleverness of the dog has been greatly increased by long 

 hereditary intercourse with man, while the cleverness of 

 the elephant, the monkey, and the opossum is all native 

 and self-evolved. The squirrel's paws stand him in 

 almost equally good stead. For though he has no 

 opposable thumb, he can hold a nut or a fruit between 

 them, rolling it about or adjusting it meanwhile : and 

 his teeth also serve as regular tools, which further enable 

 him to manipulate an object held in his paws almost as 

 well as any other animal except the apes and monkeys. 

 It is observable, too, that his tail belongs markedly to 

 one of the two types common among forestine tree- 

 haunting creatures. Those which crawl or hang among 

 the boughs have generally prehensile tails to aid them 

 in grasping the branches : those which run and leap from 

 tree to tree have generally bushy tails to aid them in 

 balancing themselves, and to act as a sort of aerial 

 rudder. In the flying squirrels and many other similar 

 exotic types the use of such tails as a parachute is supple- 



