42 Mil. T. H. HUXLEY ON THE MORPJIOLOGY OF THE CEPHALOUS JMOLLUSCA. 
The oesophagus takes a straight course backwards from the mouth, which contains 
a minute lingual prominence, and widens gradually into a pyriform muscular gizzard, 
which is provided with two strong curved and conical teeth. The intestine passes 
from the narrow pylorus, and preserving the same width throughout, bends down- 
wards towards the ventral side, and ultimately terminates in the cavity of the mantle 
a little to the left of the mesial line, fig. 6. 
Just behind the pylorus a very long straight c^cum is given off, and sometimes 
there is a short one in addition by the side of it. The parietes of these sacs are 
glandular. 
A long “columellar” muscle attaches the animal near to the apex of its shell, and 
then passes down into the foot, where it spreads out. 
The position of the heart varies remarkably in this genus, and this variation is still 
more remarkable, if, with Eydoux and Souleyet, we consider it to be one with 
Cleodora. 
In C. adculata (figs. 6, 7) Ike mantle-cavity extends considerably beyond the 
transversely-barred portion of the mantle, and the base of the auricle abuts upon its 
lower posterior portion. The apex of the heart points backwards and a little to the 
left side, and in M. Milne-Edwards’s arrangement the animal would be prosobran- 
chiate. In C. virgidata (E. and S.) the base of the auricle lies behind the right pos- 
terior portion of the mantle-cavity, and the apex of the ventricle points directly to 
the left ; it is therefore neither prosobranchiate nor opisthobranchiate. 
In Cleodora curvata, on the other hand, as will be seen immediately, the base of 
the auricle is posterior and the ventricle points forwards; it is opisthobranchiate, 
figs. 4 and 5. 
In this one genus, then, we have every transition from the prosobranchiate to the 
opisthobranchiate type of organization. 
The aorta is too delicate to be readily traced in C. virgulata and C. adculata. It 
may however be seen passing through the nervous ring and bifurcating for the epi- 
podia, fig. 7 w. There is no rudiment even of a venous system. 
The Cleodora curvata (figs. 4 and 5) (one of the true Cleodorce as formerly defined) 
forms a transition from the preceding species to Hyalaea. It has the geneial oigani- 
zation of the former, with the flattened shell more or less fissured laterally, and the 
filiform appendages to the mantle, of the latter. 
The alary expansion forms a more rounded disc than in C. adculata and virgulata, 
the metapodium having become widened out and almost imdistinguishable from the 
epipodia. The triangular lobes, rudiments of the mesopodium, have disappeared. 
The intestinal canal resembles that of the two former species ; its flexure is ventral, 
and the anus opens into the cavity of the mantle on that side. The long caecum has 
orange-coloured glandular parietes. 
The position of the heart has been described. It is comparatively large, and the 
aorta may be readily traced from it, passing forwards over the stomach and through 
