No. 3] AUDITORY OR HAIR-CELLS OF THE EAR. 453 



frequently, and on this assumption the intricacies of the 

 innervation of the auditory sense organs are readily explained. 

 When a fibre from one of the outer rows of hair-cells starts on 

 its journey to the brain it meets obstacles of several kinds, 

 and all along its course, so that the direction it is to take is 

 very much a matter of accident. One process of development, 

 above all others, determines its general course. I refer to the 

 spiral growth of the cochlea, which, during this period, is 

 actively going on, so that all fibres have this spiral twisting 

 force exerted upon them, and it results in giving many of 

 them a curved, if not spiral, course to the modiolus. As 

 growth goes on the cell is carried away from the position occu- 

 pied at the time when it started its cell process, and in this 

 way the convexity of the curve of the fibre is turned away 

 from the direction of growth. If the cell process fails to find 

 passage-way through a cell-row, or past any other obstruction, it 

 may be turned either way and grow for a greater or less dis- 

 tance before proceeding further radially. A fibre may suffer 

 such an interruption of its course several times before it 

 passes out of the organ of Corti. Another source of displace- 

 ment and plexus formation, is this — after a fibre is once laid 

 down the cells between it and its point of passage through the 

 hair-cell row or rows may increase in number, and force the 

 nerve fibre to grow in length in this part of its course, so that, 

 ultimately, what was at first only a short bend in the nerve 

 fibre becomes a long "spiral " thread. 



The so-called spiral nerve tracts of Corti's organ are, in some 

 cases, the product of the lateral brandies of the cochlear nerve 

 before leaving the organ (PI. I, Fig. 5, sp.\ PI. II, Figs. 11, 17; 

 PI. Ill, Figs. 25, 27). The main (system) collection of these 

 fibres is found below and inside of the inner hair-cells, /. e., in 

 the lymph space generally formed in this region, and which 

 has been named Nuel's canal, a name which there is no neces- 

 sity for retaining. In preparations of the fresh organ of Corti, 

 this lymph space, with its contained structures and many of 

 the adjacent cells, comes oiit as a long cylindrical structure, 

 having the appearance shown in PI. Ill, Fig. 10, of my Verte- 

 brate Ear Memoir. On PI. Ill, Fig. 28, I have sketched the 



