502 
THE OCEAN WORLD, 
many rows of hooked and pointed teeth; the nostrils are placed in 
front of the mouth. The eyes, which open in the upper part of the 
head, are half projecting, and protected in part liv a continuation of 
the soft, elastic, and retractile skin, which covers the head. Imme- 
diately behind the eyes are two blow-holes, which communicate with 
the interior of the mouth. The animal is able to open and close 
these holes at pleasure, by means of an extensible membrane, which 
Fig. 318 . The White Ray <R»ia tutis). 
acts as a sort of valve. Through these holes it ejects the superabundant 
water beyond what is necessary for respiration. In its general colour 
the animal is ashy grey on its upper surface ; white, with rows of 
black spots, below. 
Its tail is long, flexible, and slender, acting at once as a rudder and 
a weapon of offence or defence. When lying in ambush, nearly buried 
in mud at the bottom of the sea, and it has no desire to change its 
position, a rapid and sudden stroke of this formidable weapon, armed 
