H4 Anecdotal Natural History. 



is under water, and can only hear sounds that are 

 transmitted through the water. How, then, is the 

 whale to hear sounds that are made above the surface 

 and are transmitted through the air ? The difficulty 

 seems insuperable, but is overcome in the simplest 

 manner imaginable. Let us see what is the struc- 

 ture of the ear in mammalia, taking our own as an 

 example. 



First, there is an aperture for the admission of air. 

 At a variable depth in this aperture, a very elastic mem- 

 brane, called the ' tympanum,' or drum, is stretched 

 tightly across it, and is acted upon by any vibrations 

 of air which are rapid and regular enough to become 

 sounds. 



On the other side of the drum is a set of bones, 

 called, from their appearance and office, the hammer, 

 anvil, and stirrup. These take the vibrations of the 

 drum, and transmit them to the nerves of hearing, 

 through which they pass to the brain. I may incident- 

 ally mention that the modern telephone is nothing but 

 a rude imitation of the structure of the ear. 



The tube does not end at the drum, but passes on, 

 though very much reduced in size, to the back of the 

 throat. If this secondary tube (called the Eustachian 

 tube) be stopped, deafness results, because the vibra- 

 tions of the drum are checked. 



Now, in the whale the size of the two tubes is 

 reversed. The external tube is very small, but the 

 Eustachian tube is very large, and passes into the 

 nostrils, or 'blow-hole.' The aperture of this blow- 

 hole is always above water when the whale floats 

 on the surface, so that the vibrations of the air can 

 pass through it to the tympanum. Thus the whale hears 

 through the blow-hole any sounds which are caused 

 by the vibration of air, and through the external tube 

 those sounds which are caused by the vibration of water. 



