4:4 EVENINGS AT THE MICKOSCOrE. 



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

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

 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 pounce^ to rub on paper 

 from which writins: has been erased. It is this sub- 

 stance of which I mean now to speak. 



The possessor of this structm-e is a member of the 

 numerous class Mollusca, which are generally charac- 

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

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

 water : take into vour hand that larsre Cassis on the 

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

 pactness. It is, in fact, real limestone ; difiering 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. AVe will presently examine 

 other examples. The " cuttle-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, would 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 

 Bolid column. Wonderful to tell, the calcareous shell 

 is made not onlv to be no hindrance to its swimmino:, 

 but to contribute greatly to its buoyancy : it is what 

 the strins: of corks is to the bather who cannot swim — 

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



