96 LAND AND FRESH-WATER MOLLUSKS. 
only to increase their shells. With respect to 
Helicella cellaria, H. lucida, and H. nitidula, it 
was not satisfactorily ascertained whether their 
heads were buried during the process of growth.” 
The habits of the British Helices vary with the 
species; they are all terrestrial ; the majority of 
them are denizens of woods and shady places, 
climbing trees or rocks, or concealed among moss 
and under stones ; others affect open heaths and 
pastures ; a few are, as it were, domesticated ; and 
Helix aspersa has the greatest claim for the title 
of the “ Domesticated Snail ;”? some others live 
on plants growing on the margins of pools, &e. 
Independently of changes of temperature, 
the land snails have the power of becoming 
dormant at will. If asnail be deprived of food 
by placing it in a box, it will attach itself by a 
thin parchment-like secretion, or epiphragm, and 
will remain, if undisturbed, in a torpid state for 
a lengthened period. ‘There is an account of a 
snail that thus lived without food for fifteen years. 
The snail in such cases may be resuscitated by 
plunging it into lukewarm water. In their 
native haunts, they are found in this state of 
inactivity during the summer season, when there 
is continued drought, but on the first shower they 
recover and move about in search of food. Such 
as live in exposed situations necessarily become 
inactive during the heat of the day, but are up 
