5054 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
tip. This fibre and knob he considers to be the termina- 
tion of the nerve in the retinal cell. This continuity has, 
however, not yet been seen in HL. cirrosa. 
There is in both species a second region where 
pigment accumulates, towards the internal end of the 
retinal cell (fig. 86, Pzg,). 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 are 
round, of about 5 mm. 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 (Pl. X, 
ioe OG, Ol; 22.) 
The epithelial lining consists of two kinds of tall 
slender cells:—(1l) Spindle shaped cells with large 
nuclei, which are the true olfactory cells, each bearing 
externally a stiff fine process, while internally they are 
continued into fibres which run from the olfactory nerve, 
and having, external to the nucleus, an oval, finely 
vranulated body (Pl. VI, fig. 65, Olf. cell). (2) Epithelial 
cells, of long.cylindrical form, which are interspersed 
among the sensory cells (fig. 65, Hp. cell), and have their 
internal ends drawn out into fine branching processes. 
We have no evidence that this organ is really 
