154 ANATOMICAL AND PHYSIOLOGICAL STUDIES ON 



with the papilla spiralis, is not supported by my observation. 

 That the freeing of the outer zone of the membrane is not ab- 

 solutely necessary for the mediation of auditory impulses is 

 demonstrated in the cochlea of birds, as shown by Hasse ('66), 

 Retzius ('84), Sato ('17), and others. In these forms the mem- 

 brane remains through life attached to the epithelial ridge. 



My results agree with those of Hardesty ('15) on this point, 

 though he obtained a tectorial membrane which floats free in 

 the endolymph with its outer zone. Lane ('17) studied the cor- 

 relation between the structure of the papilla spiralis and the 

 appearance of hearing in the albino rat, but his description is 

 brief and does not touch on this relation of the papilla to the 

 tectorial membrane. 



Thus the inception of hearing does not coincide with the 

 detachment of the tectorial membrane from the papilla spiralis, 

 but with the development of each constituent of the papilla 

 spiralis and the membrane tectoria, as has been described. As 

 these changes occur first at the base and then pass to the apex, 

 the animal can perceive at first only the sounds of high pitch. 

 One or two days later development is complete in all the turns, 

 and then the rat can hear the sounds of lower pitch also. Thus 

 the process of the development of the cochlea does not support 

 the ' telephone theory' of audition, but on the contrary agrees with 

 the conclusion that the papilla in different locations in the turns 

 of the cochlea responds to sounds of a definite pitch, as Witt- 

 maack ('07), Yoshii ('09), Hoessli ('12), and others have shown 

 by experimental studies on the mammals. 



Concerning the exact age of the first appearance of the function 

 in the rat, there are several different statements. Lane ('17) 

 found no response to sound before the twelfth day after birth, 

 and on the sixteenth day he reports hearing well established. 

 Kreidl and Yanase ('07) state that hearing begins in the rat at 

 from twelve to fourteen days. My rats responded usually at 

 ten to twelve days, but one at nine days. These differences 

 depend in all probability on the vigor of the young during the 

 first days of postnatal life, and it seems probable that exception- 

 ally well-nourished young might develop precociously in this 



