5 8 THE BOOK OF NATURE STUDY 



as in the armadillos of South America. These bony plates form 

 a great shield over the back, and a large oval plate on the head. 

 But the middle portion of the back shield, between the fore- and 

 hind-limbs, is made up of a series of rings, so that the animal is 

 enabled thereby to roll itself up into a ball, practically defying 

 attack. This is its only means of defence against enemies, for 

 it cannot run very fast, and has no teeth, such as would be of 

 use in fighting. 



Finally, we come to the whales, porpoises and dolphins, whose 

 bodies are absolutely naked, the skin being exceedingly smooth 

 and glossy, thereby reducing friction to a minimum during 

 their movements through the water. Compensation for this 

 loss of hair is made, as we have already remarked, by a 

 tremendously thick layer of fat immediately under the skin. 



