55 
rections. T'he presence of connective tissue in the wall of the heart 
is revealed by large nuclei very regularly interspersed. The in- 
ternal cavity of those two lateral subdivions which I hold to be 
the auricles is more especially traversed by radial fibres, each of 
them enclosed in a folded sheath of connective tissue. The lateral 
walls are also very thick, whereas dorsally the muscular tunie of 
the bodywall appears partly to replace the proper walls of the organ. 
In the hinder portion of the heart I noticed a curious structure 
which I am absolutely at a loss to explain: a hollow sac, in 
the median line, 0.118 mm. in diameter, without any visible contents 
and elosed on all sides. The wall of this sac is built up by small 
cubice cells, apparently applied upon a membrane; it is never more 
than one cell thick (fig. 58). Its significance and function will 
have afterwards to be enquired into, as also the way of communi- 
cation between the cavity of the heart and the posterior tissues. 
Small local projections into the pericardium are on all sides enclo- 
sed by thin membrane and filled with blood-corpuseles: they are 
present both on the inferior surface of the heart and on the surface 
opposite, and may perhaps originate by a kind of transsudation of 
the blood-Auid through the fibrous wall of the heart. 
The dorsal sinus which in the anal region communicates with 
the heart just mentioned and takes its course dorsally along the 
genital gland, follows the curve of the bodywall anteriorly and bends 
away over the muscular pharynx (figs. 12 & 36). Just in front 
of the cerebral ganglion it divides into two, each lateral sinus ben- 
ding backwards round the pharynx though closely adhering to the 
body-wall. I could not make out the further course of these two 
trunks nor whether they collect the blood and lead it to the dor- 
sal vessel and the heart, or the contrary. Nor can I give new 
information respecting the ventral sinus. It is dorsally limited 
(fig. 24, d) by the horizontal diaphragm (v. GRAFF), posteriorly it 
appears to send its contents to the right and left of the reetum into 
the folds of its wall which were above described (figs. 13 & 32), 
whereas anteriorly the blood it contains seems to be partly collec- 
ted from the considerable lacunar cavity of the foot. Not only is 
