MUSSELS 441 



prison, owing to continued growth, but in return are well protected 

 against enemies. Hence the shells also may be so much reduced in 

 size as sometimes not completely to enclose the body. 



These features are displayed in a still higher degree by the Ship- 

 Worm {Teredo navalis). This animal has more the appearance of a 



Marine Lamellibkanchs. (Natural size.) 



M., M., Sea-mussels, sessile, on a submerged tree-trunk, with foot protruded and byssus threads. 

 The "crimped" structures are the mantle-edges protruding between the valves. A., Oysters 

 of different ages, sessile, upon a rock (these figures seem to be wrongly drawn, the oysters 

 are represented as attached by the right or Hat valve instead of the left) ; H., cockle with 

 protruded foot and fringed incurrent and excurrent siphonal tubes ; at HI, one of the latter 

 buried in the sand, with only the two tubes left protruding ; next to it another cockle with 

 the shell closed, seen from the dorsal or hinged side, and on the right one of the valves of 

 a cockle-shell. 



worm (name) than of a mollusc, and bores long galleries in piles and 

 other woodwork. It often does great damage hj destroying wooden 

 structures in harbours and breakwaters, and also by burrowing into the 

 hulls of ships, which on that account are covered over with copper. 



