IXX INTRODUCTION. [CH. 



nomenon may perhaps be classed. I have no doubt 

 that both of these mysteries will in due time become 

 equally obsolete and superseded by some other preter- 

 natm'al manifestation. 



Injuries to Man. — The sum total of the mischief in- 

 flicted by the MoUusca upon Man is easily told and 

 reckoned; and it by no means counterbalances the 

 benefit he derives from them. At sea, the damage done 

 to the woodwork of our piers by some kinds of ship- 

 worm [Teredo), as well as by species of an allied genus 

 [Xyhphaga), is indeed not inconsiderable ; and, before 

 copper or yellow-metal sheathing was used for protect- 

 ing the bottoms of our outward-bound vessels, these 

 marine scourges used to be justly dreaded. The noble 

 breakwater at Plymouth has also suffered, although not 

 to any extent, from the excavations made in its more 

 exposed parts by a small bivalve [Saxicava rugosa) ; and, 

 on some parts of the coast, beds of clay, which served as 

 natural barriers to ward off the action of tidal waves on 

 om' harbours, have disappeared in consequence of Pho- 

 lades having chosen to take up their abode in them. On 

 land, our molluscan foes are more troublesome than 

 formidable. Turnips and cabbages occasionally suffer 

 from the partiality of slugs to such succulent food ; and 

 of course we cannot help sympathizing with the gentle 

 florist who sees her pet carnation nipped in the bud and 

 ruined, in consequence of its having been selected by a 

 hungry or dainty snail for its supper. But the wire- 

 worm, fly, and grub are far more formidable pests to the 

 farmer and gardener, and no mollusk has been known 

 to attach itself parasitically to Man ; so that we may 

 safely challenge the entomologist in favour of the com- 

 paratively harmless subjects of this inquiry. Various 

 remedies have been proposed for preventing the ravages 



