WILD LIFE OF ORCHARD AND FIELD 



glacial period, the melted ice reclaimed the shallows, 

 the snails would be left colonized upon the high 

 points now widely separated by water. 



More casual circumstances have always con- 

 tributed to this world-wide distribution. Snails 

 frequently conceal themselves in crevices of bark, 

 or firmly attach themselves to branches and foliage, 

 and thus might be drifted long distances, since 

 they are able to resist starvation for an immense 

 period, and to protect themselves against injury 

 from salt-water or excessive heat by means of oper- 

 cula and epiphragms; violent storms might fre- 

 quently transport living shells a considerable dis- 

 tance, and aquatic birds do carry them and their 

 eggs from pond to pond attached to feet or plu- 

 mage. 



The astonishing vitality of the snails in every 

 stage of existence favors the theory that they endure 

 such accidental means of travel and thrive at the 

 end of it. Edward S. Morse records that he has 

 seen certain species frozen in solid blocks of ice af- 

 terwards regain their activity; and others enduring 

 an equal extreme of heat without any bad effect. 

 They have been shut up for years in pill-boxes, 

 or glued (seven years in one case) to tablets in mu- 

 seums, and yet a trifle of moisture has been suffi- 



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