UNIVALVE MOLLUSC A. 419 



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 Testacella, is very exactly indicated by 

 Nature. Lifnax 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 Limax rufus. 



The Helicidse 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 it is 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 stomacli. 



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 



B B 2 



