24 Our British Snails 



of those which we shall find in England, the 

 common garden snail Helix aspersa, and a fresh- 

 water mussel, Unto margaritifer, and see where 

 they come in the scale of creation and what are 

 their powers and peculiarities. 



Molluscs {mollis esca, soft food — boneless crea- 

 tures) are below the aristocracy of the vertebrates 

 or backboned creatures, and so they come just 

 below the Fishes, but above the Insects. They 

 are divided into those possessing a head and 

 those possessing no head (although with some sort 

 of a brain or organ of sense), the snail being of 

 the former class and the mussel of the latter. 

 The former are univalves and the latter bi- 

 valves having two shells for protection. The 

 latter also are restricted to life in w^ater, 

 whereas the former are found both on land and 

 in water, e.g. the snail and the whelk, although for 

 ages probably no molluscs were air-breathing 

 land dwellers. In the class of Cephala, to w^hich 

 our snail belongs, there is the sub-class of Gastero- 

 poda, or stomach-footed, because on the ventral 

 side of the body a sole-like disc or foot exists, 

 by the wave-like expansions and contractions 

 of which the animal progresses. 



In this sub-class there is a division accord- 

 ing to their having or not having an operculum, 

 or means of closing and protecting the orifice 

 of the shell. Most gasteropods which live in 

 water have this ; most which live on land (only 



