LATERAL CANAL SYSTEM OF SELACHIANS 29 



The usual manner of distribution of the nerve fibers to the 

 groups of hair-cells is shown in figure 5. The fibers run along 

 the basement membrane until they reach points beneath the 

 particular groups of hair-cells which they innervate. Here 

 they usually make a sharp bend and, losing their medullary 

 sheaths, they penetrate the basement membrane (fig. 13), but 

 in several cases they are seen to divide into two or more primary 

 divisions while still outside of the sensory epithelium (figs. 17, 

 20, 21). The nerve fibers may divide at a variety of levels be- 

 tween the longitudinal fiber zone and the bases of the hair-cells. 

 As a rule the finer fibers pass deeper into the sensory epithelium 

 before dividing than the larger ones, but fibers of intermediate 

 sizes are seen dividing at various levels between the basement 

 membrane and the hair-cells. The primary branches of a single 

 nerve fiber separate rather widely, and as seen in longitudinal 

 section (fig. 12) they may cover approximately the base of one 

 group of hair-cells. These branches divide repeatedly, often into 

 extremely fine fibrillae which pass freely between the adjacent 

 walls of the hair-cells to a distance ranging from about one- 

 foiU"th to three-fourths or more of the length of the hair-cells 

 (figs. 13, 16, 20). In a great number of cases the fibrillae are 

 seen to terminate in little rounded enlargements or end-knobs, 

 and varicosities of similar appearance occur at various levels on 

 many of the terminal branches (figs. 13, 19). The largest are 

 often seen at points of prmiary division and in some cases re- 

 semble the terminal enlargements of the ampullae of the ear 

 described by MuUenix (1910) as 'calyses', though they do not 

 bear the same relationship to the hair-cells as Mullenix has 

 suggested they do in the auditory epithelium of Fundulus. 



No cup-like expansions or close anastomosing networks around 

 the bases of the hair-cells have been observed. The appearance 

 of such conditions in the auditory epithelium, as reported by 

 some investigators, seems likely to have been due to overstaining 

 or over-impregnation, with resulting irregular deposits of silver 

 between the finely dividing fibrillae. 



The general similarity between the canal organs and those of 

 the internal ear makes the nature of the terminations of the 



