by a
membrane, and hanging loosely in the viscero-pericardial chamber, is
the pyriform sac of Owen. This has been shown to be the rudimentary
left oviduct or sperm-duct, as the case may be (E.R. Lankester and
A.G. Bourne), the functional right ovi-sac and its duct being attached
by a membrane to the opposite side of the heart.

The cephalic and abdominal aortae of _Nautilus_ appear, after running
to the anterior and posterior extremes of the animal respectively, to
open into sinus-like spaces surrounding the viscera, muscular masses,
&c. These spaces are not large, but confined and shallow. Capillaries
are stated to occur in the integument. In the Dibranchs the arterial
system is very much more complete; it appears in some cases to end in
irregular lacunae or sinuses, in other cases in true capillaries which
lead on into veins. An investigation of these capillaries in the light
of modern histological knowledge is much needed. From the sinuses and
capillaries the veins take origin, collecting into a large median
trunk (the vena cava), which in the Dibranchs as well as in _Nautilus_
has a ventral (postero-ventral) position, and runs parallel to the
long axis of the animal. In _Nautilus_ this vena cava gives off at the
level of the gills four branchial afferent veins (fig. 11, v.c.),
which pass into the four gills without dilating. In the Dibranchs at a
similar position the vena cava gives off a right and a left branchial
afferent vein, each of which, traversing the wall of the corresponding
renal sac and receiving additional factors, dilates at the base of the
corresponding branchial plume, forming there a pulsating sac--the
branchial heart. Attached to each branchial heart is a curious
glandular body, which may possibly be related to the larger masses
(fig. 11, r.e) which depend into the viscero-pericardial cavity from
the branchial afferent veins of _Nautilus_. From the dilated branchial
heart the branchial afferent vessel proceeds, running up the adpallial
face of the gill-plume. From each gill-plume the blood passes by the
branchial efferent vessels to the heart, the two auricles being formed
by the dilatation of these vessels.

The blood contains the usual amoeboid corpuscles, and a diffused
colouring matter--the haemocyanin of Fredericque--which has been found
also in the blood of _Helix_, and in that of the Arthropods _Homarus_
and _Limulus_.