464 The Outline of Science 



means of these they move cautiously along, back downwards, 

 hanging to the underside of the branches. It is interesting to 

 notice how many features of these strange creatures have been 

 altered in relation to their upside-down mode of progression. 

 Thus they can bend their head round so as to look downwards 

 over their shoulder; the neck is very mobile, and in some species 

 has nine instead of the usual seven vertebrae; the shaggy hair 

 hangs down in a unique way, and its suggestion of a mass of 

 fibrous plants may be enhanced by the presence of a green Alga. 

 One of the most effective adaptations to arboreal life is the 

 most familiar namely, the prehensile tail of many monkeys. 

 In the Spider Monkey (Ateles) the tail is used not only to 

 support the whole body, but actually as a "fifth hand" for grasp- 

 ing the food. Again, we get an impression of the plasticity of 

 animal structure the same part being turned and twisted to 

 so many different uses. 



The Squirrel 



It may be doubted if there is any climbing mammal with 

 more all-round attractiveness than the Common Squirrel. It is 

 small without being pigmyish; the bushy tail balances the body; 

 the rich brown-red upper colouring is very pleasing; the ear- 

 tufts present during the colder half of the year make the creature 

 look even more alert than it is; its movements take one's breath 

 away. 



Its table manners are perfect, for it sits upright, holding its 

 food daintily in its hands; it neatly unshells the kernel of the 

 nut; it even removes the thin outer pellicle before it begins to 

 munch. Everyone knows how the squirrel passes from tree to 

 tree, but it may also press its body against the stem and remain 

 perfectly still. When it sleeps it uses its tail as a blanket. The 

 security of its life probably adds to the gaiety of its disposition, 

 for it is one of the playing animals, enjoying what looks like 

 "tig" among the branches. Squirrels usually pair early in spring. 



