MOLLUSCA 205 
Thus, in this animal at least, and probably in all Molluscs, 
the cavity of the generative organs and of the glandular part 
of the kidney is part of the coelom, and the generative cells 
are formed from coelomic epithelial cells. 
Branch B. EUTHYNEURA. 
CHARACTERISTICS.—The second great branch into which the 
Gasteropoda Anisopleura is divided differs from the Strepto- 
neura in the fact that the torsion of the visceral hump has 
proceeded to a less extent, and that consequently the peri- 
cardium 1s placed obliquely in front of the mantle cavity and 
gul. For the same reason also the one side of the visceral loop 
has not become pulled over the other by the forward rotation 
of the gill and osphradium, and the loop is untwisted. The 
condition of the gill and kidneys is as in Azygobranchiata. 
The right auricle is wanting. With one exception, no 
operculum is found. All Euthyneura are hermaphrodite, a 
sharp distinction from the Streptoneura. The shell is often 
but slightly caleified, and it and the mantle tend to disappear. 
The Euthyneura comprise two orders: (i.) the Opistho- 
branchiata and (i1.) the Pulmonata. 
The Opisthobranchiata are characterised, as their name 
implies, by the position of the ctenidium behind the heart. 
The branchial vein opens into the auricle, which is situated 
behind the ventricle. The shell is often absent, and when it is 
developed it is frequently covered by a fold of the mantle. 
Both the mantle and the ctenidium may, like the shell, be 
wanting, the function of the ctenidium may be carried on by 
processes of the body-wall. 
In some Opisthobranchs the margin of the foot is produced 
into two broad flaps, which may stand out at right angles to 
the axis of the foot, or may in some cases be folded up against 
the sides of the body. 
One of the most characteristic features of this order is the 
presence of processes of the body-wall termed cerata or dorsal 
papillae. The cerata vary very much in size, number, and 
arrangement. Processes of the liver are proloneed into some 
of them, these have been termed hepatocerata to distingusih 
