34 MARINE AND AQUATIC TRESPASSERS. 



under the ice. He instantly strikes a heavy blow on 

 the ice with the back of his axe, which stuns the animal 

 almost as effectually as if the blow had been dealt 

 directly ; so that a hole can be cut in the ice, and the 

 lifeless body lifted out. 



Now with the whales, a very difficult problem has 

 to be solved namely, to make a mammalian ear that 

 is capable of hearing sounds below the surface, and 

 yet will not be too sensitive, and will not admit water. 

 The first difficulty is solved by the manner in which 

 the internal ear is constructed. That portion of the 

 temporal bone in which the organ of hearing is placed 

 does not form part of the skull, but is quite separate, 

 and only held in its place by ligaments. Next, the 

 orifice of the ear is exceedingly small ; so tiny, indeed, 

 as almost to escape observation. In spite of the 

 enormous size of the whale, the external aperture is 

 so small that a crow-quill can hardly be introduced 

 into it. 



The most remarkable part of the organ is yet to 

 come. 



We have seen how the animal is enabled to hear 

 sounds which are transmitted through the water, and 

 the wonderful manner in which the auditory organs 

 are modified for that purpose. 



But another problem now arises. As the animal 

 spends a considerable portion of its time on the 

 surface, it must also be able to hear sounds which are 

 transmitted through the air, lest it should be surprised 

 by foes which are out of the range of its vision, and 

 which it is unable to detect by hearing. The tiny 

 apertures which serve perfectly well for the trans- 



