278 AVERS. [Vol. VI. 



and it is just as incorrect to speak of our hearing the vibrations 

 of the air as it would be to say that we hear the vibrations of 

 the string or bar or tongue or other music (sound) producing 

 instrument without mediation. At all times and under all 

 circumstances vertebrate animals have ]ieard, if at all, by means 

 of disturbance of sensory hairs projecting from the morphologi- 

 cal surface of the body into the water in which they lived. 

 Now, in the lower forms, e.g. some fishes, the essentially sac- 

 like ear is open to sea-water, and when the outer opening was 

 finally closed, it must have been in some form whose ear was 

 at one time open to the supernatant water ; so that it is more 

 than a figure of speech to say that before emerging upon land 

 the vertebrate type fitted its ear for the step by shutting up the 

 outer opening of the endolymphatic duct, thereby retaining and 

 perpetuating an aquatic condition essential for the surviving 

 sense organs of the auditory type. Indeed, these auditory organs 

 owe their survival to such closing up of the auditory sac and 

 to a sufficient and permanent supply of a watery medium for 

 the support of the sensory hairs. This is due to the fact that 

 it is impossible to construct so delicate a mechanism to oper- 

 ate in the air. The organ arose in aquatic ancestors, and the 

 physical requirements remaining the same, the organ must of 

 necessity acquire a liquid chamber in the head to replace that 

 originally supplied by the sea. 



Wherein does the difference in the physiological function of 

 the auditory sense organs consist } Does it lie entirely in the 

 structural differences between the various organs of the audi- 

 tory complex or entirely in the structural differences of the 

 central terminations, or in both combined .'' 



The general consensus of physiological opinion at the present 

 day is in favor of the third view. As every one knows, the sense 

 organ may be cut off from its central connection, and still the 

 characteristic sensation be felt, and the central organ may be 

 so destroyed that although the sense organ and its centripetal 

 conductors are intact, still under stimulation no sensation may 

 be aroused. It is evident, I think, that we shall never be quite 

 certain that a difference in structure of the sense organ necessi- 

 tates a difference in physiological functions until we shall suc- 

 ceed in grafting on to the nerve of one special sense the sense 

 organs belonging to another special sense, as, for example, in- 



