13 



August! "' ■ ■■ rifort, if one examines unprotected v/ooden 

 structures submei'iF;ed in the water very small bivalves will 

 be round crawling actively over t!ie surfaces. These are 

 very minute and are easily recognized as "Siiip-worm" lar- 

 vae v/hat have just settled upon the wood. The larva moves 

 rapidly in search of a favorable place for attachraent, and 

 this is usually in some minute depression or crevice in 

 the wood, though it may also become attached to perfectly 

 smooth surfaces. It seems to possess no organ of special 

 sense for the purpose, and yet, it is able to determine 

 what places are favorable for its futuji'e life, and to 

 avoid those which are not. Once it lias chosen a point for 

 attachment, it tlirows out a single long byssus thread, 

 v/hich secures it at the surface of the v/ood, and soon los- 

 es its velum, so so that it can no longer lead a free life. 

 Once attached, the larva bo "-ins to clear avmy a place, by 

 scraping av;ay the surface of the wood with the ventral 

 edges of its shell valves. Small particles of \rood and 

 other substances, that are thus formed, are cemented togeth- 

 er over the larva so as to form a sort of conical covering 

 for protection. This formed, the transformation of the 

 larva into the small "L^.iip-worm" begins and progresses rap- 



