MOLLUSCS. 



285 



'^1 



J 



an at-ciileiit sunk a coastino- boat iwwv St. Si'ljastian in S])aiii. Four months later some 



fishermen raised the vessel, hoping to turn the materials to advantage, if not to rejiair 



the vessel itself, but in the short space of time that hud 



elapsed, the planks and thnbers vfere so completely riddled 



by the Teredos that they were valueless. There is a curious 



fact noticed in connection with theu- burrowing. No 



matter how many of these molluscs gain entrance to the 



same piece of wood, their tubes never interfere with one 



another, but there is always left at least a thin j)artilion 



i>et\veen two adjacent burrows. 



Since their appearance in Holland so long ago, these ship-worms 

 have done an incredible amount of damage to wharves, ships, etc., 

 .md many devices have been suggested for checking their ravages. 

 The use of chemicals, creosote, etc., has but comparatively slight 

 effect, for since these animals do not eat the wood, the chemicals do 

 not jioison them. While kyanising (soaking the wood witli creosote) 

 is an effectual check against that injurious crustacean, the gribble 

 (Limnoria Ugnorum), it is but a slight defence against the Teredo. 

 In Xorway, timbers which were saturated with creosote under a 

 ])ressure of ten pounds to the square foot were found two years 

 later to be filled with the molluscs. To iron rust they have a de- 

 cided a\ersiiin, and piles and other timbers which are driven full of 

 l)road-headed nails escape their ravages. Our modern vessels also 

 escape their injurious action, thanks to 

 the (;opper sheathing with which their 

 hulls are covered. On our coasts south 

 of Cape Cod, it is customary to coat all 

 spars and buoys with verdigris })aint, 

 and to take them up every six months 

 for cleaning and a' new coat of this 

 poisonous paint. Notwithstanding this, 

 the average life of a buoy is only about 

 twelve years, but half of which is spent 

 in the water. 



On our coast. Teredo navaUs is the 

 most common and most injurious sjn- 

 cies, but tliree other si>ecies of Tered 

 and one of Xylotriju, an allied genu^ 

 occur in larger or smaller numbers. In 

 tropical waters many other forms occui, 

 of which we need only mention T 

 rorniformis, which bnrrows in tin fic in— ri. *>,/(»- 



■ ?((/is, hhij) worm. 



hu^ks of cocoa-nuts and other wi)od\ 

 fruits floating on the sea, and the gigantic Scptaria 

 areuaria, of the Philippine Islands, which burrows in 

 the sand, sometimes attaining a diameter of two inches 

 and a length of nearly six feet. 



J'holas and its allies are also burrowing forms, but, unlike those just luentioncd, 



1* 



\1fl 



>y 



Fig. 3U. — Teredo : 



