252 
ZOOLOGY. 
The singular aarcl-vark or Orycteropns (0. capensis, 
Fig. 292) inhabits Soutli 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 tlie 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 due to the fact that the pulp is persistent; the 
enamel in front causes them to wear away behind so that 
Fig. 292.— Orycteropus. From Lutken's Zoology. 
they are chisel -shaped. The species are prolific, live mostly 
on vegetable food, and are of small size; the muskrat, 
beaver, and capybara 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 {My odes) 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 
