^S AVERS. [Vol. VI. 



the chamber. These cells were, however, of low stage of dif- 

 ferentiation, not raised above the cells of the maculae sacculi 

 and utriculi in physiological capabilities, and consequently the 

 limit was soon gained for a useful multiplication of the sensory 

 structures in this way. If a few cells could do all the work of 

 the many and subserve other functions at the same time, it 

 would be of advantage to the animal to reduce the number of 

 cells, conserve its nerve energy, and gain in perfection of 

 service. 



Just this has been done in the transformation of the Saurop- 

 sid cochlear organs into the mammalian condition, but at the 

 same time the length of the narrowed series has been greatly 

 increased, so that information is reported to the brain from a 

 hundred independent sources in the mammal ear where it was 

 reported from ten in the Sauropsid ear, serially speaking ; for 

 the important condition of sequence is concerned only when 

 the reporting cells are at different distances from the brain. 

 Where all the cells are the same distance from the brain, they 

 speak practically as one. 



There is then a repetition of canal-organ arrangement in the 

 cochlear organ of the Mammalia, and this is indicated by the 

 nerve supply, the blood supply, the separation of the end cells 

 themselves, and by all the subordinate structures that have been 

 impressed with the structural relations of the sense organs and 

 their connections. In PL XII, I have attempted to illustrate 

 in a perspective view the existing condition of things in the 

 human ear. 



The structure of the hair-bearing cells in the cochlea of the 

 mammalian ear has been a subject for difference of opinion ever 

 since their discovery. 



Waldeyer and Gottstein describe them as twin cells com- 

 posed of upper and lower halves, the parts corresponding to 

 the hair cells and the supporting cells of other authors. I have 

 never found a double or twin cell among my many preparations, 

 and I do not believe in their existence. The hair cells as I 

 have found them correspond to the upper halves of the twin 

 cells of Waldeyer and Gottstein, the hair cells of Retzius and 

 of Paul Meyer. 



The hair cells of the outer rows are larger than those of the 

 inner. They are cylindrical in shape and filled with a clear fluid 



