Introduction, 



■•a;s*5s^«*?^ 



2a 



called fins. The cuttle-fish and slug are examples which will 

 give you a general notion of the naked tribes ; and with the 

 great variety in the shelled species you are now familiar. 



At the first glance, you might suppose that such creatures 

 can be productive neither of much benefit nor much injury to 

 man ; but a little detail will convince you that this would be 

 ^4iasty conclusion. 



V The catalogue of their " injuries," I must acknowledge, is 

 riot extensive. The slug (Z/imax) and snail (Helix hor- 

 tensis) {fig, l,a\ the gardener will inform you, frequently 



destroy, and perhaps always more or less injure, his early 

 crops, while they mutilate and render disgusting the fruits of 

 autumn : but the farmer often finds them a more serious pest ; 

 for in spring they often issue, in inconceivable numbers, from 

 their concealments on a dewy eve, and feed upon the young 

 and tender crops. No kind of herbage seems unpalatable to 

 them, but to clovers they give a preference ; and the damage 

 they annually do to them and to turnips is really very great. 

 Many fields were this summer made barren by them, and 

 more ^ were so thinned as to require to be resown. 



Of the marine tribes the Teredo navalis {Jig, 7. b\ or Ship- 

 worm, is the only one which has excited notice by its destruc- 

 tive powers. This shell-enclosed worm, which Linnaeus has 

 emphatically, yet not undeservedly, styled the " calamitas 

 navium,*' is said to have been introduced into our seas from 

 the East within little more than a century. They are now 

 common in all the seas of Europe ; and being gifted with the 

 power of perforating wood, they have done, and continue to 

 do, extensive mischief to ships, piers, and all submarine wooden 

 buildings. The soundest and hardest oak cannot resist them ; 

 but, in the course of four or five years, they will so drill it, as 

 to render its removal necessary, as has happened in the dock- 

 yard of Plymouth. In the years 1731 and 1732, the United 



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