86 



tip. This fibre and knob lie considers to be the termina- 

 tion of the nerve in the retinal cell. This continuity has, 

 however, not yet been seen in E. eirrosa. 



There is in both species a second region where 

 pigment accumulates, towards the internal end of the 

 retinal cell (fig. 86, Pig^)- The pigment here is connected 

 with the larger basal accumulation by a long slender 

 track. This track and internal accumulation surround 

 the nerve fibre and knob, according to Hesse. 



In the dark, e.g., at night, the pigment all collects 

 at the base of the cells, but during the daylight much 

 flows up from here, and collects at the apex of the cells, 

 and so protects the delicate visual cells from excess of 

 light. 



The Olfactory Organ. 



Eledone has one pair of olfactory pits. These arc 

 round, of about 3 nun. diameter, and situated just inside 

 the mantle cavity, in the angle between the postero-lateral 

 wall of the funnel and the mantle. Hence they cannot 

 easily be seen in the living specimens. They are shallow 

 pits, lined by horizontally folded epithelium (PI. X, 

 fig. 66, olf. P.). 



The epithelial lining consists of two kinds of tall 

 slender cells : — (1) Spindle shaped cells with large 

 nuclei, which are the true olfactory cells, each bearing 

 externally a stiff Hue process, while internally they arc 

 continued into fibres which run from the olfactory nerve, 

 and having, external to the nucleus, an oval, finely 

 granulated body (PI. VI, fig. 65, Olf. cell). (2) Epithelial 

 cells, of long cylindrical form, which are interspersed 

 among the sensory cells (fig. 65, Ep. cdl), ami have their 

 internal ends drawn out into fine blanching processes. 



We have no evidence that this organ is real I \ 



