foot in the male as compared with
the female nautilus is not confined to the existence of the spadix.
The anti-spadix and the reduction of the inner inferior lobe are also
male peculiarities. The external annular lobe in the male does not
differ from that of the female; it carries nineteen tentacles on each
side. The four ophthalmic tentacles are also present. Thus in the male
nautilus we find altogether sixty-two tentacles, the thirty-two
additional tentacles of the female being represented by lamelliform
structures.

_Musculature, Fins and, Cartilaginous Skeleton._--Without entering
into a detailed account of the musculature of _Nautilus_, we may point
out that the great muscular masses of the fore-foot and of the
mid-foot (siphon) are ultimately traceable to a large transverse mass
of muscular tissue, the ends of which are visible through the
integument on the right and left surfaces of the body dorsal of the
free flap of the mantle-skirt (fig. 1, l, l, and fig. 3, k). These
muscular areae have a certain adhesion to the shell, and serve both to
hold the animal in its shell and as the fixed supports for the various
movements of the tentaculiferous lobes and the siphon. They are to be
identified with the ring-like area of adhesion by which the
foot-muscle of the limpet is attached to the shell of that animal. In
the Dibranchs a similar origin of the muscular masses of the fore-foot
and mid-foot from the sides of the shell--modified, as this is, in
position and relations--can be traced.

[Illustration: FIG. 7.--Minute structure of the cartilage of _Loligo_
(from Gegenbaur, after Furbringer)

a, Simple cells.

b, Dividing cells.

c, Canaliculi.

d, An empty cartilage capsule with its pores.

e, Canaliculi in section.]

In _Nautilus_ there are no fin-like expansions of the integument,
whereas such occur in the Decapod Dibranchs along the sides of the
visceral hump (figs. 15, 16). As an exception among Octopoda lateral
fins occur in _Pinnoctopus_ (fig. 38, A), and in _Cirrhoteuthis_ (fig.
38, D).

In _Nautilus_ there is a curious plate-like expansion of integument in
the mid-dorsal region just behind the hood, lying between that
structure and the portion of mantle-skirt which is reflected over the
shell. This is shown in fig. 2, b. If we trace out the margin of this
plate we find that it becomes continuous on each side wit