enal sacs
give off each a diverticulum dorsalwards, which unites with its fellow
and forms a great median renal chamber, lying between the ventral
portions of the renal organs and the viscero-pericardial chamber. In
_Loligo_ the fusion of the two renal organs to form one sac is still
more obvious, since the ventral portions are united. In _Octopus_ the
renal sacs are quite separate.

_Gonads and Genital Ducts._--In _Nautilus_it has been shown by E. Ray
Lankester and A.G. Bourne that the genital ducts of both sexes are
paired right and left, the left duct being rudimentary and forming the
"pyriform appendage," described by Sir R. Owen as adhering by
membranous attachment to the ventricle of the heart, and shown by W.
Keferstein to communicate by a pore with the exterior. The ovary
(female gonad) or the testis (male gonad) lies in _Nautilus_, as in
the Dibranchs, in a distinct cavity walled off from the other viscera,
near the centro-dorsal region. This chamber is formed by the coelomic
or peritoneal wall; the space enclosed is originally part of the
coelom, and in _Sepia_ and _Loligo_ is, in the adult, part of the
viscero-pericardial chamber. In _Octopus_ it is this genital chamber
which communicates by a right and a left canal with the renal sac, and
is the only representative of pericardium. The ovary or testis is
itself a growth from the inner wall of this chamber, which it only
partly fills. In _Nautilus_ the right genital duct, which is
functional, is a simple continuation to the pore on the postero-dorsal
surface of the membranous walls of the capsule in which lies the ovary
or the testis, as the case may be. The gonad itself appears to
represent a single median or bilateral organ.

The ovary forms a large projection into the genital coelom, and the
coelomic epithelium is deeply invaginated into the mass of the gonad,
so as to constitute an ovarian cavity communicating with the coelom by
a narrow aperture. The ova originate in the epithelium, migrate below
it and then, as they enlarge, project into the ovarian cavity, pushing
the epithelium before them. Each ovum is surrounded by a follicular
epithelium which is nourished by numerous blood-vessels, and which
penetrates into the surface of the ovum in numerous folds. When
mature, the ovum is contained in a membrane or chorion with a
micropyle, and escapes by dehiscence of the follicle into the