24. FRIENDS WORTH KNOWING. 
Mountains. At any time, nevertheless, an artificial raising 
of the temperature breaks the torpor, the warmth of the 
hand being enough to set the heart beating. Extreme 
drouth also will cause snails to seal their doors hermetically, 
without even hanging a eard-basket outside. This is to 
shut off the evaporation of their bodily moisture, and hap- 
pens in midsummer; hence it is termed estivation. Cer- 
AN EDIBLE SNAIL. 
tain foreign slugs (Testacellidee) which have no shells, are 
able to protect themselves under the same circumstances 
by a gelatinous appendage of the mantle, which, in ease of 
sudden change of temperature, can be extended like an 
outer mantle, so to speak, from its place’ of storage, un- 
der the “buckler,”’ and having wrapped themselves, they 
burrow into the soil. These carnivorous testacelles are 
