ON PTEROPODA. 319 
on each side, and by no means on its lateral parts, which cor- 
respond to the lateral parts of the sheath, neither does it pre- 
sent any trace of the arrangement of gills. Those which 
Cuvier has described and figured as such, are really only 
the muscular fibres of the lateral prolongations of the mantle. 
As in its central parts, this envelope is very thin, one may 
perceive, transversely, above, the true gill on the right side, 
and the ovary forming a much more considerable mass to the 
left. All the lower part is occupied by the liver, and the 
second portion of the oviductus. 
The anterior or cephalo-thoracic part of the hyalxa is 
much more complicated. It is separated from the posterior 
by a very sensible contraction, which has been named 
erroneously a neck, from whence it has followed that the 
divers organs which are found there have been mistaken. 
The fact is that we must distinguish there the trunk properly 
so called, terminated anteriorly by the head, which is not 
separated from the foot, or from the locomotive appendages, 
which are enormously developed on its sides. 
The trunk consists in a very narrow band, but little distinct, 
and especially so underneath ; for above it forms perceptibly 
enough, an oval, elongated, plane projection, between the 
locomotive appendages, and is terminated by the head. The 
extremity of the male apparatus of generation, is even seen a 
little behind, through the skin, which is very thin. On this 
part, and at its anterior extremity, are the tentacula. They 
are rather small, but very visible, cylindrical, and formed by 
a sort of sheath, in which are contained the true tentacula, a 
little swelled at their summit. 
The existence of eyes in this animal has not been precisely 
ascertained, but it appears very probable. 
More in front, and a little to the right, at the root of the 
tentaculum on that side, is an orifice a little infundibuliform. 
