252 ZOOLOGY. 



The singular aard-vark or Orycteropns (0. capensis, 

 Fig. 292) inhabits South Africa, and is timid and nocturnal 

 in its habits, feeding on white ants. 



Order 2. Glires (Rodentia). — The rats, squirrels, porcu- 

 pine, and beaver are common examples of this extensive 

 group. They differ from animals of other orders in the 

 large incisor teeth and in the absence of canine teeth. The 

 feet are adapted for walking and climbing or burrowing, 

 the claws being long and curved. A peculiarity in the in- 

 cisors is that they grow out as fast as they are worn down; 

 this is clue to the fact that the pulp is persistent; the 

 enamel in front causes them to wear away behind so that 



Fig. 292.— Oryctoropus. From Liitken's Zoology. 



they are chisel -shaped. The species are prolific, live mostly 

 on vegetable food, and are of small size; the muskrat, 

 beaver, and eapybara being the largest members of the 

 order. The flying squirrels (Fig. 293) take short flights 

 by means of the expansion of the skin between the fore 

 and hind legs, gliding from tree to tree as if supported by 

 a parachute. They are only active at night. 



The Norway lemmings (Myodes) are noticeable for 

 their remarkable migrations from the elevated plateaus of 

 Scandinavia down and into the sea; the object and origin 

 of which are inexplicable, and are not indicative of much 

 intelligence. While the true lemming has very small but 



