92 THE WORLD OF ANIMAL LIFE 



thick layer of stiff, stout bristles. We do not see these in the 

 " seal-skin " of a lady's cloak, because they are carefully removed 

 in one of the processes by which the skin is prepared for use. But 

 in the living animal they are easily noticeable, and as they are 

 continually lubricated by a kind of oil, which is secreted by a 

 number of tiny glands in the skin, they form, as it were, a kind of 

 waterproof greatcoat. 



Beneath this is another layer of much softer and finer hairs, 

 which lie closely against the skin, and form, when thoroughly 

 cleansed and prepared, the ordinary " seal-skin " of commerce. 

 These, too, are lubricated by the natural oil, so that the icy water 

 in which these animals spend so much of their lives can never 

 come into actual contact with the skin. 



The skin itself, too, is considerably modified, for it is from two 

 to three inches thick, and contains a great number of cells filled 

 with oil, like the well-known " blubber " of the whale. Now, oil is 

 an excellent non-conductor of heat; that is, it will not allow heat 

 to pass freely through it. Thus, the seal is protected from the icy 

 chill of the water in which it swims, first, by the outer layer of 

 thick, stiff bristles; secondly, by the inner layer of soft, warm fur; 

 and thirdly, by the thick, blubber-like skin. 



How do seals swim? If we look at one of them as it glides 

 through the water, we cannot detect its method of propulsion. 

 It does not paddle itself along with its flippers, but seems to move 

 in any direction at will, without putting forth any kind of exertion. 



But if we look a little more closely, we shall see that the two 

 flattened hinder feet are pressed closely side by side together, so as 

 to form a single broad oar. By means of this oar the animal swims. 

 It is well known that a boat can be propelled by a single oar, 

 worked to and fro in the water from the stern. Now, if we look 

 upon the body of a seal as a boat, we shall see that the animal 

 propels itself along by simply turning its natural oar from side 

 to side in the water. 



The form of a seal's body, too, is well adapted for swimming, 

 for it is that of a pointed cylinder; and this shape, which 

 offers the least possible amount of resistance, is common to all 

 creatures which fly through the air, tunnel through wood, burrow 



