The adult organisation of Paragordius varius. 433 
The medio-ventral cavity (M.V.Cav Figs. 61, 63, 64, 
Pl. 40; Fig. 65, 66, 70, Pl. 41) extend further forward than the others, 
and backwards as far as the anterior end of the cloaca. Most anteriorly 
(Fig. 61, Pl. 41) it appears as a simple slit between the parenchym 
(L. Par) above and the nerve cord (N.C) and intestine (Int) below. 
More posteriorly its space increases in size, and throughout the greater 
region of the trunk it is a voluminous space in the mid-ventral line 
above the intestine and nerve cord, bounded dorsally and laterally by 
the mesenteries (Mes), and ventrally by the ventral deflected portion 
of the latter which covers the nerve cord. Posteriorly (Fig. 68) the 
receptaculum seminis (Rec) when distended nearly fills this space. 
The significance of this cavity will be considered again under the 
section “supraintestinal organ’. 
None of these cavities communicate with the exterior, nor with 
the cavities of the ovaries, uteri or intestine. 
The mesenteries. There are two dorso-ventral mesenteries 
(Mes Figs. 63, 64, Pl. 40; Fig. 66, Pl. 41), which extend through the 
greater length of the trunk, one on each side of the median plane, 
and each enclosing dorsally a uterus (Ut). They are closely pressed 
against each other when the ovaries are full of eggs and the uteri 
empty; but when the ova have passed into the uteri they become 
more separated, except those portions of them which bound the median 
surfaces of the uteri. Dorsally they are separated by the medio- 
dorsal body cavity (M. D.Cavw), ventrally by the medio-ventral cavity 
(I. V. Cav), and each is attached to the body wall dorsally and ven- 
trally. In the anterior region of the trunk (Fig. 61, PJ. 40; Fig. 65, 
Pl. 41) there are no mesenteries, the large-celled parenchym taking 
their place; the mesenteries first become delimited with the appearance 
of the body cavities. Posteriorly also the mesenteries disappear with 
the disappearance of the body cavities (Fig. 70, Pl. 41), so that they 
may be said to be defined and delimited by the uteri and the body 
cavities. They do not envelope the intestine, in which respect they 
differ from the mesenteries of Annelids. 
The parenchym. This peculiar tissue occurs under a number of 
modifications, but everywhere has the nature of connected masses of 
. mononucleated cells, with a dense intercellular substance, the latter 
constituting a network of closed spaces within which the cells lie 
(Par., L. Par Figs. 13, 14, Pl. 37; Figs. 15—17, Pl. 38; Figs. 61, 63, 
64, Pl. 40; Figs. 65, 66, 68, 70—75, Pl. 41). The nuclei are generally 
large and with numerous true nucleoli, also rich in chromatin; the 
