44 EVENINGS AT THE MICEOSOOPE. 



yellow sands kissed by the rippling waves, tlie shell, or 

 bone as it is sometimes called, of the Cuttle-fish. You 

 know that it consists of a shallow boat-shaped shell, 

 the hollow of which is filled with a white substance, 

 which can be scraped away even with the finger-nail, 

 and which is sometimes use as ^ounoe, to rub on paper 

 from which writing has been erased. It is this sub- 

 stance of which I mean now to speak. 



The possessor of this structure is a member of the 

 numerous class Mollusca, which are generally charac- 

 terised by being inclosed in shells. ISTow shell, as we 

 all know, is a solid, stony substance, much heavier than 

 water ; take into your hand that large Cassis on the 

 mantel-piece, and observe its great weight and com- 

 pactness. It is, in fact, real limestone ; differing from 

 that of the rocks only in this, that it has been depos- 

 ited by the living organic cells of an animal, and ar- 

 ranged in a definite form. "We will presently examine 

 other examples. The " cxittle-bone " is a shell, not in- 

 deed inclosing the animal, but inclosed by it ; being 

 contained within a cavity in the substance of the fleshy 

 mantle ; cut open the mantle, and the shell instantly 

 drops out. 



The Cuttle is a rapid swimmer through the open 

 sea. A shell so large as this, if solid and compact like 

 that of the Cassis, woixld condemn it to grovel on the 

 bottom, and frustrate all the instincts of its nature. On 

 the other hand, it needs the strength and support of a 

 solid column. Wonderful to tell, the calcareous shell 

 is made not only to be no hindrance to its swimming, 

 but to contribute greatly to its buoyancy : jt is what 

 the string of corks is to the bather who cannot swim — ■ 

 it is a float. Throw this entire cuttle-shell into water ; 



