242 A NATURALIST IN HIMALAYA 



method. I place the organ out of action by fixing the 

 tip of the tail to the back of the squirrel's neck. I 

 again place it on the smooth bar. It makes vain 

 attempts to keep its balance ; the tail struggles with 

 its bonds in the endeavour to break free, and the 

 squirrel may end by tumbling completely over, clinging 

 with flexed claws to the under surface of the bar. 

 Thus the main function of the tail is as an organ of 

 equilibrium. It is a pliant wand gradually developed 

 to its present length to enable its owner to keep its 

 balance while it leaps and clambers through the trees. 



On occasions the flying squirrel completely inverts 

 the normal position of its body and hangs back down- 

 wards from the under surface of a branch. The 

 tail, under such conditions, becomes curled round the 

 branch from which the animal is suspended, and its 

 position cannot but suggest to the mind that it actually 

 is employed as an organ of support. Indeed it 

 would only require a slight increase in the muscular 

 tension in order to become so. Now in this striking 

 attitude we may possibly detect one of the evolutionary 

 gradations in the development of the prehensile tail, 

 a trace of a gradual passage from an organ of 

 equilibrium to an organ of prehension, from an organ 

 which in the flying squirrel maintains a balance in 

 the tree to one which, as in the American monkeys, 

 actually grasps the branch in order to sustain the 

 body. 



When the flying squirrel glides through the air 

 its tail is held rigid and trailed out behind. It has 

 been considered on these occasions to act as a kind 

 of a rudder by which the animal can guide its move- 

 ments and actually change direction when in the 



