genital
coelom and duct. In its passage to the exterior the ovum passes a
glandular structure on the wall of the genital capsule, which probably
secretes the gelatinous substance enclosing the eggs. In addition to
this internal gland there are other accessory glands, which are not
related to the genital duct or sac but are differentiations of the
wall of the pallial cavity, and occur on the inner wall of the pallium
in _Nautilus_, on the somatic wall in Dibranchiata. In _Nautilus_ they
form a continuous mass. These produce the external envelopes of the
eggs.

In the male the testis is a specialized portion of the wall of the
genital coelom, and has a structure comparable to that of the ovary.
The spermatozoa pass through an orifice from the cavity of the testis
to the genital capsule, and thence to the spermiduct. The spermiduct
is provided with a glandular pouch, and opens into a terminal
reservoir known as Needham's sac or the spermatophore sac. The
function of this pouch is to form the spermatophore, which is an
elastic tube formed of structureless secretion and invaginated into
itself. The deeper part contains the spermatozoa, the external part is
called the connective, and is usually much contracted and spirally
coiled. When the spermatophore is expelled into the water the
connective is extended and evaginated, and the sac containing the
sperms bursts. In _Nautilus_ the spermatophore when uncoiled is a
little over 30 mm. in length. These spermatophores are somewhat
similar to those formed in certain pulmonate Gastropods.

The eggs are laid shortly after copulation. In _Nautilus_ they are
laid separately, each being about 4 cm. long and contained in two
thick shells, the outer of which is partly open.

[Illustration: Fig 13.--Nervous system of _Nautilus pompilius_ (from
Genebaur, after Owen).

t, t, Ganglion-like enlargements on nerves passing from the pedal
ganglion to the inner series of tentacles.

t', Nerves to the tentacles of the outer or annular lobe.

b, Pedal ganglion-pair

a, Cerebral ganglion-pair.

c, Pleuro-visceral ganglionic band (fused pleural and visceral
ganglion-pairs).

d, Genital ganglion placed on the course of the large visceral
nerve, just before it gives off its branchial and its osphradial
branches.

m, Nerves from the pleural ganglion to the mantle-skirt.]

_Nervous System