332 SUPPLEMENT 
tentaculum, and proceeds to fix itself at the extremity. This 
muscle, by its contraction, draws in the horn, turning it inside 
out, like the finger of a glove.. These organs, on the contrary, 
are unfolded by the action of the annular fibres of the skin 
which forms them. The mouth and its appendages are 
drawn back by another muscular bundle from the pillar of 
the shell; and they are put forth by some small muscles, 
much shorter, which, from the circumference of the lip, ter- 
minate on the anterior edges of the mouth. 
Of the interior anatomy, we shall merely notice the organ 
of respiration. This is situated in a large cavity, placed 
above the general mass of the viscera, occupying the last 
whorl of the shell. It communicates with the external air 
by an orifice formed in the right side of the thick edge of the 
mantle, or in the collar. All the inferior part of this cavity 
is smooth, and formed by a membrane evidently muscular ; 
but the superior is almost entirely vascular. 
Thus the snail, like all the mollusca of the same family, 
respires directly the atmospheric air in a cavity evidently 
pulmonary. The mechanism of this function is simple 
enough. The animal causes the air to enter, by drawing 
back the respiratory cavity into the last whorl, which is the 
broadest, at the same time putting forth from the shell, all 
the parts that can come out, and strongly dilating the pulmo- 
nary orifice; it expels the air, on the contrary, by withdraw- 
ing its body into a more narrow part of the shell, and by so 
much the more completely, as it draws in the head, foot, &c. 
But these movements of respiration are never regular. The 
fluid elaborated in the respiratory organ, or the blood, which 
is of a slightly bluish white, arrives to the heart, by means of 
the pulmonary vein. | 
These animals, like the slugs, are hermaphrodite, giving 
and receiving fecundation at the same time. The organs of 
