THE AMERICAN NATURALIST. [Vol. XXXVII. 



lying immediately interna] to the ear-drum and connected with 

 the mouth by the Eustachian tube. Through the cavity of the 

 middle ear a bridge of small bones, the ear ossicles, passes from 

 the ear-drum to the opposite wall of the middle ear where the 

 innermost ossicle abuts against the cavity of the internal ear. 

 The internal ear, which is situated somewhat deeper in the head 

 than the middle car, is a complicated fluid-filled sac with three 

 semicircular canals and a spirally twisted portion, the cochlea. 

 The nerve concerned with the sense of hearing ends in the walls 

 of this sac. When the ear is normally stimulated, the sound- 

 waves from the surrounding air beat against the ear-drum and 

 set it in vibration. These vibrations cause the chain of ossicles 

 to vibrate and thus the motion is handed on to the fluid of the 

 internal ear. This fluid vibrates in turn and by some process 

 not clearly ascertained stimulates the nerves on the walls of the 

 ear-sac. As is well known the deafness caused by injuries to the 

 external and the middle ear may often be relieved by various 

 mechanical contrivances, but injuries to the internal ear are of 

 an absolute kind and not open to amelioration, for the internal 

 ear, as its nerve connections show, is the true organ of hearing, 

 the middle and external ears being only means of conducting 

 sound-waves to the true sense organ. 



The form of ear just described is found only in the higher 

 vertebrates; in the lower ones this organ presents a somewhat 

 simpler structure. Thus, in the frog, there is no external ear, 

 but the ear-drum is exposed directly on the surface of the head 

 and the whole auditory apparatus consists of only the middle and 

 the internal ear. In fishes a still further reduction takes place 

 in that the middle ear as such is not developed. Thus the fishes 

 possess only the essential part of the organ of hearing, the 

 internal ear, and even this is in an altered form, for their ear- 

 twisted part, the cochlea. 



generally admitted by the older observers. Thus Isaac Walton, 

 in his "Complete Angler" (1653), when asked if trout can see 

 at night replies " Yes, and hear and smell too." He then 



