CHAPTER XVI 

 SEA-SHELLS OiN THE SEASHORE 



ANY hard coat or covering enclosing a softer material 

 is called a "shell" — thus we speak of an egg-shell, 

 a nut-shell, a bomb-shell, and the shell of a lobster. But 

 there is a special and restricted use of the word to in- 

 dicate as " true " and " real " shells the beautiful cover- 

 ings made for their protection by the soft, mobile animals 

 called Molluscs. These animals expand and contract 

 first this and then that region of the body by squeezing 

 the blood within it (by means of the soft muscular coat 

 of the sac-like body) into one part or another in turn. 

 There is not enough blood to distend the whole animal, 

 and accordingly one part is swollen out and protrudes 

 from the shell, whilst another shrinks as the blood is 

 propelled here or there by the compressing muscular 

 coat. These creatures are the Molluscs, a name which 

 has come into general use (and has even served as the 

 title for a stage-play), as well as being the zoologist's 

 title for the great division of animals which they constitute. 



They are sometimes called " shell-fish," but this is 



no good as a distinctive name — since it is applied in 



the fish-trade to lobsters, crabs, and shrimps as well as 



to Molluscs. Lobsters, crabs, and shrimps are Crustacea, 



and totally different in their architecture and their 



mechanism from Molluscs. Familiar examples of 



Molluscs are the oyster, the mussel, the various 



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