ON GASTEROPODA. 329 
mals, and in spite of this sacrifice, many among them deny the 
reality of the fact, which others assert to have taken place. 
It is, in fact, impossible for any one who has not convinced 
himself of it by personal experiment, to believe in the repro- 
duction of a part so important as the head. Nevertheless; 
even now, at the present day, many persons believe it, though 
it seems to be proved that it never takes place but when the 
horns, or that part of the head which is in front of the brain, 
alone has been removed. The animal infallibly dies, when 
the first ganglion, which essentially constitutes the head, has 
been taken away. 
The motion of the limaces is in general very slow. It has 
even passed into a proverb. They have a great number of 
enemies among the birds, quadrupeds, and reptiles. Accord- 
ingly an immense quantity of them is destroyed every year, 
but the following spring amply makes up for the deficiency. 
In treating of the HELICES, or snaz/s, an interesting and 
well known genus of mollusca, we shall enlarge a little on 
the text. 
The organization of these animals has many relations with 
that of the limaces, or slugs. ‘To form an idea of it we may 
conceive one of the latter, 7.e. an ovaliform, elongated body, 
convex above, plane underneath, in which the mass of the 
viscera of digestion, and a part of those of generation, should 
have formed a sort of hernia, for the extent of the middle third 
of ‘the back, or rather in the space formed by the shield, and 
have drawn along with them the skin, considerably attenu- 
ated. This mass, in the front of which is the apparatus of 
respiration, is turned spirally, and is contained in a shell of the 
same form. 
The body is pretty nearly cylindrical in all its anterior 
parts, and, behind, terminates in a sort of tongue, entirely 
muscular, which is only the elongation of the foot. This last 
name is given to a flatted and very thick portion of the under 
