TJie Pholas. 529 



ends, and terminated in front by a point ; it is white 

 and chalky in its appearance, and the anterior end is 

 roughened by numerous sharp spines and tubercles. 

 The animal which inhabits this shell bores deeply into 

 the rocks of the sea-shore, forming cylindrical holes, in 

 which it lives ; and the water which it requires for its 

 food and respiration is conveyed to and from the 

 interior of the shell by a pair of tubes which reach to 

 the outer orifice of its dwelling-place. It is supposed 

 that the Pholas is enabled to bore into the hard rock by 

 means of its large and strong foot, but this is still a 

 matter of dispute. 



There are many other boring shells, most of which 

 are related to the Pholas. Some of them burrow in 

 rocks, others in wood, and some indifferently in either 

 material. Of the wood-borers, the most remarkable is 

 the Ship Worm (Teredo navalis), which penetrates deeply 

 into floating or submerged timber, and lines the cavity 

 of its burrow with a coating of shell. In this way the 

 Teredo has often done much injury to piles and other 

 woodwork exposed to the sea, and in 1731 and 1732 it 

 excited so much alarm in Holland by attacking the piles 

 of the great dikes, that even statesmen condescended to 

 study its natural history. We must remember, however, 

 that in the grand economy of nature even this destruc- 

 tive creature has its use ; by penetrating in every direc- 

 tion through any floating mass of timber it promotes the 

 breaking up of the latter, arid prevents the surface of 

 the sea from being encumbered with quantities of 

 wreck. 



