LAND SNAILS. 97 
and doing soon after the dew begins to fall. 
For these reasons a collector should remember, 
**it is the early bird that catches the worm,” and 
be on the alert after rain. 
Cold acts much in the same respect as heat, 
for in all temperate latitudes the majority of the 
Helicidee hybernate ; they then form a more dense 
epiphragm, and retreat farther into the interior of 
the shell than during their daily repose; ina 
few species the epiphragm is strengthened with 
carbonate of lime. During this winter sleep the 
animal functions are nearly suspended ; respira- 
tion is still carried on, and airis admitted to the 
animal by a minute perforation in the epiphragm 
opposite the respiratory orifice. 
Land shells are most abundant on limestone - 
soils, which are most congenial to their existence 
and perpetuation; and in explanation I would 
observe: firstly, that the shell is composed almost 
entirely of carbonate of lime; secondly, the 
plants upon which the snail feeds are the sources 
from whence the mineral matters are derived 
thirdly, that plants affecting calcareous soils con- 
tain proportionately a larger amount of salts than 
_ those inhabiting clayey or sandy soils, and such 
are therefore in greater request among mol- 
luscan life; so also many species of horse-tails, 
and grasses which contain a large percentage of 
earthy salts, are much frequented by land snails. 
H 
