WILD LIFE OF ORCHARD AND FIELD 



however, seem to hibernate very httle ; Vitrina, for 

 example, may be seen active in pretty cold weather, 

 and even crawling about in the snow, while the 

 finest American specimens live high up on the 

 Rocky Mountains. At any time, nevertheless, an 

 artificial raising of the temperature breaks the tor- 

 por, the warmth of the hand being enough to set 

 the heart beating. Extreme drought also will cause 

 snails to seal their doors hermetically, without 

 even hanging a card-basket outside. This is to 

 shut off the evaporation of their bodily moisture, 

 and happens in midsummer; hence it is term- 

 ed aestivation. Certain carnivorous foreign slugs 

 (T estacellidae) which have no shells, protect them- 

 selves under the same circumstances by a gelati- 

 nous appendage of the mantle, which, in case of 

 sudden change of temperature, can be extended 

 like an outer mantle, so to speak, from its place of 

 storage under the "buckler." Having enwrapped 

 themselves, they burrow into the soil. 



Snails are found in the most barren deserts and 

 on the smallest islands all over the globe, reach 

 near to the line of permanent snow on mountains, 

 and are restricted only by the arctic boundary of 

 vegetation. There is a great difference between the 

 snails of the tropics and those of high latitudes — 



304 



