ganglion.

ped, Pedal ganglion.

pl, Pleural, and visc., visceral region of the pleuro-visceral
ganglion.

gang. stell, The right stellate ganglion of the mantle connected by
a nerve to the pleural portion.

n.visc, The right visceral nerve.

n.olf, Its (probably) olfactory branches.

n.br, Its branchial branches.]

The vas deferens is at first narrow and convoluted, then dilates into
a vesicula seminalis at the end of which is a glandular diverticulum
called the prostate. By the vesicula and the prostate the
spermatophores are formed. These have a structure similar to those of
_Nautilus_, and in the Octopoda may be as much as 50 mm. in length.
Beyond the prostate the duct opens into a large terminal reservoir
which has been called Needham's sac, and in which the spermatophores
are stored.

_Nervous System and Sense-Organs._--The figures (30, 31, 32)
representing the nerve-centres of _Octopus_ serve to exhibit the
disposition of these parts in the Dibranchiata. The ganglia are more
distinctly swollen than in _Nautilus_. In _Octopus_ an infra-buccal
ganglion-pair are present, corresponding to the buccal ganglion-pair
of Gastropoda. In Decapoda a supra-buccal ganglion-pair connected with
these are also developed. Instead of the numerous radiating pallial
nerves of _Nautilus_, we have in the Dibranchiata on each side (right
and left) a large pleural nerve passing from the pleural portion of
the pleuro-visceral ganglion to the mantle, where it enlarges to form
the stellate ganglion. From each stellate ganglion nerves radiate to
supply the powerful muscles of the mantle-skirt. The two stellate
ganglia are connected, except in _Sepiola_, by a transverse
supra-oesophageal commissure, which represents the pallial cords
united by a commissure above the intestine in Amphineura. The nerves
from the visceral portion of the pleuro-visceral ganglion have the
same course as in _Nautilus_, but no osphradial papilla is present. An
enteric nervous system is richly developed in the Dibranchiata,
connected with the somatic nervous centres through the buccal ganglia,
as in the Arthropoda through the stomato-gastric ganglia, and
anastomozing with deep branches of the visceral nerves of the
viscero-pleural ganglion-pair. It has been especially described by A.
Hancock in _Ommatostrephes_. Upon the stomach it forms a single large
and read