2^6 AVERS. [Vol. VI. 



equilibrative in function. No part of the ear then constitutes 

 a special organ of equilibration, of spatial sense, or of special 

 motor control. The ear as a whole — and only because it con- 

 tains sense organs, and they only because of their hair-bearing, 

 nerve-connected cells — shares with other sense organs these 

 important functions because of common association with motor 

 and other centres, and has as its special function the perception 

 of wave motion {i.e. changes in stress) in the circumambient 

 water or other aqueous fluid, never of any other medium. 

 Where the transformation of the motions thus transmitted to 

 the auditory hairs takes place will be considered further on. 



If the reader accepts this conclusion as to the function of the 

 semicircular canals, he will certainly recognize in it an excellent 

 illustration of the results which physiologists may hope to get 

 from the careful study, not alone of adult structure, but of onto- 

 genetic changes of structure. More than half a century of 

 physiological experiment had failed to give the solution of the 

 canal problem which the first study of their phylogenesis in 

 connection with their comparative ontogeny at once revealed. 



3. Theories of Audition. 



It is proposed to restate in this chapter some of the problems 

 of auditory physiology and to consider how much and in what 

 manner they are affected by the additions to our morphologi- 

 cal knowledge already treated of in chapter B. Hensen wrote, 

 in 1879, " Helmholtz hat die Physiologic des Ohrs so tief 

 und zugleich so umfassend bearbeitet, dass seine Lehren dies 

 Gebiet mit Recht beherrschen," and one may readily satisfy 

 himself that they are generally accepted by an inspection of 

 the text-books and special papers on the subject. 



Since I consider the oitter and Diiddle ear to be mere accessory 

 structures acqidred by the higher vertebrates in ever-increasing 

 complexity for the sole purpose of enabling the animal to preserve 

 in the aerial ocean, on or near the bottom of which they live, the 

 necessary aquatic conditions in which they were born {phyloge- 

 netically) and which they must preserve or lose their auditory 

 organ completely, it follows that it will be unnecessary to enter 

 into an account of them in a discussion concerning the essentials 

 of the auditive processes, and I may as well say at once, that 

 according to my view of their functions, evcjy sense organ in the 



