UNIVALVE MOLLUSCA. 4I9Q 
of as forming the point of transition between Limax and Helix. This 
passage from Limaceans entirely destitute of shells to those furnished 
with a very small shell, as in Zestacedla, is very exactly indicated by 
Nature. Limax rufus, spoken of above, presents, under the posterior 
part of the cuirass, calcareous, unequal, isolated granulations, which 
are, so to speak, the elements, as yet internal, of a shell which is on 
the point of being built. Other species in the same genus present 
under the cuirass a little rough, imperfect scale, which seems to be 
produced by a great number of those calcareous granulations, which 
show themselves in an isolated state in Lémax rufus. 
The Helicidee is the last family we have to consider of this order. 
It is only necessary to witness the snail as it creeps along the 
gravel walks of a garden, or in the damp alleys of a park, in order to 
see that itis a being of higher organisation than the headless molluscs. 
The common snail (Helix aspersa) goes and comes; it roams and 
Fig. 191.—Testacella hahotoides (Draparnaud). 
saunters after its own peculiar manner, searching for its food or its 
pleasure ; it has a head and two prominent tentacles, which feel and 
seem to express their sensations; it has nerves, a brain, a strong 
mouth, and a well-formed stomach. 
Without possessing a high order of intelligence, the snail is by no 
means an imbecile ; it knows very well how to choose a tree the 
fruit of which is agreeable to it. A fine cluster of grapes, a succulent 
pear, which the horticulturist devours with his looks, and hopes to 
devour otherwise, is sure to be the identical fruit which will be chosen 
by our enlightened depredator the snail. 
The body of the snail is oval, elongated, convex above, flat below. 
The convex or upper surface of the body is rugged, in consequence 
of the existence of numerous tubercles projecting slightly, and sepa- 
rated by irregular furrows; its anterior is terminated by an obtuse 
head, its posterior more flat and less pointed. All the flat portion, 
thick and soft, and upon which the animal moves itself by a creeping 
motion, bears the name of “foot.” The head is not really very 
distinct, especially in the upper part; but the organs with which it 
is provided are prominent. These organs are in reality tentacles, 
although they are more popularly known as Horns, especially among 
BB 2 
