236 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
and bears a somewhat crescentic patch of pigmented epi- 
thelium (Hp.op.); the other lip, which is turned away from 
the wall of the siphon, is sharp, and is raised up to form a 
screen. The nerve branch entering the tentacle from the 
posterior pallial plexus runs in the axial part, and at the 
summit swells out into a nearly globular ganglion (Ga.op.) 
consisting of large, clear, oval cells and a network of fibres. 
On the siphonal side of the tentacle this ganglion lies close 
to the wall. It is invested on all sides except towards the 
tip and the outer wall by a capsule of fibrous tissue, which 
stains deeply and homogeneously with staining reagents, 
has no nuclei, and shows little indication of cellular nature. 
On the tip of the tentacle the hair cells, referred to above, 
can be traced into the tissue of the ganglion. Nerve fibres 
from the latter probably spread round the edge of the 
incomplete fibrous capsule, not through its tissue. 
The cells covering the tentacle generally are cubical in 
form with a continuous cuticle. Towards the tip, how- 
ever, they become higher and columnar in shape, and the 
cuticle becomes less evident. On the pigmented spot the 
outer two-thirds of each of these columnar cells is filled up 
with brownish pigment, which takes the form of a dense 
mass of spherical granules lying perfectly free from each 
other. The nucleus is in contact with the lower layers of 
this mass of granules, but is usually quite free. The cell 
body seem to be composed of clear cell substance, in which 
are embedded the round pigment granules. Beneath the 
nucleus it is faintly fibrillar, the direction of the fibrille 
being that of the long axis of the cell. A narrow space 
separates this epithelium from the capsule surrounding 
the ganglion, and this space is filled by fine fibrous tissue. 
It is very probable that nerve fibres from the ganglion, 
passing round the edge of the capsule, form part of this 
layer, and some at least terminate in or among the cells 
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