No. I.] THE VERTEBRATE EAR. 275 



mits the vibration to the system of rods. There is doubtless a 

 rod, not only for each tone, or semitone, but even for much 

 more minute divisions of the same, so that every sound causes 

 its own particular rod to vibrate. 



As the foregoing amply indicates, students of auditory physi- 

 ology, especially that of the cochlea, have thus thought along 

 two sharply defined lines, the one school holding that the rods 

 of Corti, the fibres of the basilar membrane or other of the non- 

 sensory structures, were the percipient elements, while the other 

 school claimed that the nerve end hair cells, by means of the 

 hairs which they put forth, are alone the percipient elements. 

 The rods of Corti were made to do duty as the percipient struc- 

 tures by Helmholtz in his earlier studies, because the hair cells, 

 as such, had not been discovered by Corti or his immediate suc- 

 cessors, and they looked upon the rods as the essential elements 

 of the organ. The basilar membrane (fibres) was afterwards sub- 

 stituted by Hensen and at once adopted by Helmholtz, because 

 from their insufficient knowledge of its structure, it appeared 

 not only admirably suited but apparently specially designed for 

 this very function. Hasse for the lower vertebrates, and Meyer 

 for the whole group, denied this function to the basilar mem- 

 brane, because they found animals with a cochlea without a 

 suitable basilar membrane, but supplied with hair cells. 



The subject has never been explained with lucidity from the 

 comparative anatomical standpoint, and so the Hensen-Helm- 

 holtz "piano-string" theory has held the field against all comers. 

 Although some students, like Foster, considered it inadequate, 

 and others, like Rutherford, not content to leave matters as they 

 were, offered new solutions of the difficulty, it is not probable 

 that any general advance could have been made in physiological 

 ideas in this field until a broader view of the whole matter had 

 been taken, based upon increased anatomical and embryological 

 knowledge. 



It is a necessary consequence of the canal organ parentage of 

 the ear sense organs, that they inherit functions similar to those 

 of the parent organ, modified only in individual ways, as off- 

 spring always are modified in some degree. 



The great similarity, on the other hand, of the offspring, 

 among themselves and to their parent, would enable any one of 

 them to take on the functions of one or more of its fellows — 



