46 Journal of Comparative Neurology. 



body which takes a deeper stain than the inner cuticular layer 

 — a stain like that of the outer cuticular layer. The inner end 

 of this apparent rod joins the apex of the spiral organ ; the 

 outer end is sometimes bluntly rounded, but more often flares a 

 little (Plate II, Fig. 45). Careful study seems to show that this 

 apparent rod is an artefact. Very often the cuticular canal ap- 

 pears to be a mere opening through the cuticula without distinct 

 walls of its own ; then again it often appears to be lined by a 

 distinct layer which takes a deeper stain than that of the sur- 

 rounding cuticula. Finally cases are often found in which the 

 lower parts of the more deeply stained lines along the two mar- 

 gins of the canal have separated from the inner layer of the 

 cuticula (Plate II, Fig. 44). It may also be seen, both in sec- 

 tions of prepared material and in the surface views of living 

 material, that the outer layer of the cuticula thins out and dips 

 down into the flaring outer end of the canal ; moreover, in 

 macerations, the central tube always remains attached to the 

 cuticula. All of these various appearances have led me to the 

 conclusion that the central tube of the spiral organ passes en- 

 tirely through the canal in the inner layer of the cuticula, the 

 tube normally being closely pressed, perhaps actually joined to, 

 the sides of the canal. The appearance of a rod in this canal is 

 due to reagents, which cause the outer end of the central tube 

 to shrink partly or wholly away from the cuticular canal in 

 which it lies and to assume a rod-like form. This interpretation 

 is borne out by the fact that this apparent rod has never been 

 found in living material — the central tube always appearing 

 empty throughout its length. The dipping down of the outer 

 layer of the cuticula into the outer end of the cuticular canal 

 suggests that the central tube of the spiral-organ is an invagina- 

 tion of the outer cuticula — an invagination probably formed be- 

 fore the formation of the inner layer of the cuticula. If, as 

 now seems probable, the outer layer of the cuticula is either 

 shed or worn away, the outer end of this central canal must each 

 time either shift its attachment or else the inner surface of the 

 canal itself must disappear and the cells of the spiral organ 

 secrete new cuticular material. 



