15 
in the skin and readily come off in the mouths of such ani¬ 
mals as may attack them, thus forming a terrible means of 
defense to the animal. The ease with which these spines 
are detached has, without doubt, given rise to the fable that 
the Porcupine was able to shoot forth its quills, like arrows, 
against its foes. 
The Flying Squirrel (Pteromys volucella ) is a pretty little 
Rodent found throughout the United States, east of the Mis¬ 
souri river. Its aerial progression is merely a leap, prolonged 
by means of a fold of skin stretching between the fore and 
hind limbs on each side, which expands and bears the animal 
up for a short distance, after the manner of a kite. 
The Vulpine Phalanger (Phalangista vulpina) and the 
Yellow-bellied Phalanger (.Belideus flaviventer ) are small, 
vegetable-eating marsupials (see page 43) from Australia; 
the common cassowary, 
