X96 INTRODUCTION. 
their original bulk in a moist situation. 1 In all these 
instances the young have been developed in the same 
manner as in other eggs not subjected to the experiment. 
In the northern part of the United States we have fre- 
quently observed the eggs of the Helicidce in the forest 
covered -with snow, protected only by a single leaf, where 
they had remained through the winter months, constantly 
exposed to a temperature much below the freezing point. 
The Helicidce themselves withstand the cold of the sever- 
est winters in the same situations ; and Succinea has 
been frozen in a solid block of ice, and yet escaped 
unharmed. Helices, when frozen in a state of confine- 
ment, though they sometimes recover so far as to move 
about with some activity, usually survive but a short 
time. 
The power of reproduction of parts of the body is more 
astonishing still. It is well established by experiments 
on thousands of Helices, that the tentacles, when cut off", 
grow out again, — that considerable parts of the loco- 
motive disc may be amputated, and the new parts imme- 
diately bud out, and supply their place. The great length 
of time they can subsist without food is another exempli- 
fication of their great tenacity of life. Those species, 
especially, which live in dry and exposed situations have 
this power of endurance to a remarkable degree. A 
friend received specimens of if. desertorum which had 
been collected in Egypt, had been shipped to Smyrna, 
thence to Constantinople, thence to Rio Janeiro, and 
1 Leuclis, loe. cit. 
