30 FRIENDS WORTH KNOWING. 



The astonishing vitality of the snails in every stage of 

 existence favors the theory that they endure such acciden- 

 tal means of travel and thrive at the end of it. Professor 

 Morse records that he lias seen certain species frozen in 

 solid blocks of ice, and afterward regain their activity ; and 

 enduring an equal extreme of heat, where the sun's rays 

 crisped the leaves for weeks together, without any bad ef- 

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

 for years (seven years in one case, Dr. Newcomb, of Cornell 

 University, told me) to tablets in museums, and yet a trifle 

 of moisture has been sufficient to resuscitate them. They 

 survive so well being buried in the ballast of ships that at 

 every seaport, almost, you may find species imported in that 

 way, which came to life when the ballast was dumped at 

 the time of unloading. That birds occasionally carry them 

 about is well verified. 



Such are some of the methods of dispersion. Yet stu- 

 dents are obliged to confess that the causes of the present 

 puzzling geographical distribution of land shells are so com- 

 plex that we can hardly hope to determine them with much 

 exactness. 



As to the longevity of snails, little is known ; but some 

 individuals no doubt attain great age. Some species of 

 cylindrella have a habit of deserting the point of the spire 



