LAND SNAILS. 
97 
and doing soon after the dew begins to fall. 
For these reasons a collector shonld 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 
Helicidce hybernate ; they then form a more dense 
epiphragm, and retreat farther into the interior of 
the shell than during their daily repose; in a 
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 air is 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 
