LIMNORIA LIGNOHUM. 355 



The means taken to protect the woodwork are of 

 several descriptions, viz., copper sheathing ; iron nails 

 closely studded ; (the ferruginous oxide that the action 

 of sea-water produces, impregnates the wood, and forms 

 a protective iron crust all over the surface ;) creosote 

 and coal-tar are likewise used, and it is the opinion of 

 Mr. Moore that all timber that can be smeared over once 

 a year, is effectually freed from the ravages of the 

 Limnoria. 



The action of these animals is more or less rapid, 

 according to circumstances. Pinewood they appear to 

 destroy about the rate of one-quarter to half an inch 

 in a year : of course this must be less rapid during 

 the first year or so, and more rapid after several years, 

 for the numerical increase of animal life must be 

 greater in proportion to time. We find that that portion 

 of the pine framework that supports the hull of the 

 Robust frigate, that was commenced being built on the 

 31st of October, 1859, and is submerged at every tide, 

 has been eaten in many places from two to three inches, 

 while an inspection of the pine scaffolding round the 

 half-built fort just within the Plymouth breakwater and 

 harbour, erected between three and four years, shows us 

 that the extent of the depredation amounts to from 

 three-fourths of an inch to an inch and a half, according 

 to the nature of the wood and its freedom from any pro- 

 tecting influence. The little animals invariably choose 

 the softer places, shunning the knots and hard lines of 

 wood that longitudinally connect one knot with another. 

 They likewise avoid every part of the wood that had 

 been impregnated with iron, sometimes for several inches 

 round the place where a nail or bolt had been driven. 



Oak they attack not so readily as pine, but still the 

 former gradually falls before their persevering action, the 



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