530 



wood as feldom as poiTible; for after it has penetrated 

 a little way, it turns, and continues with the grain, tole- 

 rably ftrait, until it meets with another fliell, or per- 

 haps a knot, which produces a flexure: its courfe then 

 depends on the nature of the obftruflion, if confiderabie, 

 it makes a fliort turnback in form oi sl Jj'pho7i, rather 

 than continue any diftance acrofs the grain. 



We had an opportunity of examining a great number 

 of thefe {hells in the Dock-Yard of Plymouth; where 

 every means have been tr-ied to prevent the deftruftive 

 quality of thefe pernicious animals, which are now be- 

 come naturalized to the climate, and have increafed con- 

 fiderably, though fuppofed to be of oriental origin. 



The piles we examined had been recently taken up to 

 be replaced with new ; thefe we were informed, had not 

 been under water above four or five years, and though 

 perfeftly found and folid oak, were greatly perforated.* 



It mud be prefumed, that the tube is lengthened as 

 the animal's growth requites ; and that it can extend the 

 whole length of the perforation without quitting the tail : 

 but that it cannot recede far, by reafon of the increafe 

 of the anterior valves affixed to the head, and the taper 



fl^ape 



* The method now adopted to preferve ,the timbers necefTarily ufed about 

 tlie docks, is to cover that part which is continually under water, with fhort, 

 broad-headed nails, which in fait water, foon cover every part with a ftrong 

 coating of rufl, impenetrable to thefe animals: and we are afTured this has 

 been found to fucceed better than flieathingwith copper. 



