THE OYSTER. 25 



surface of the shell. When broken out it is found to 

 be coated with a thick plate of white shell, which is 

 beautifully smooth and pearly upon the side nearest the 

 glass. 



Microscopic examination of this plate shows that it 

 is made up of an immense number of minute crystals, 

 packed and crowded together into a solid mass, with- 

 out any regular arrangement. These observations 

 show that the new layers are thrown off in the form 

 of a gummy excretion from the mantle, with the lime 

 in solution, and that the particles unite with each other 

 and form crystals while the gum is hardening. 



The oyster obtains the lime for its shell from the 

 water, and while the amount dissolved in each gallon 

 is very small, it extracts enough to provide for the 

 slow growth of the shell. It is very important that 

 the shell be built up as rapidly as possible, for the 

 oyster has many enemies continually on the watch for 

 thin-shelled specimens. In the lower part of the bay 

 I have leaned over a wharf and watched the sheeps- 

 head moving up and down with their noses close to 

 the piles, crushing the shells of the young oysters 

 between their strong jaws and sucking out the soft 

 bodies. As I have watched them I have seen the juices 

 from the bodies of the little oysters streaming down 

 from the corners of their mouths, to be swept away by 

 the tide. 



The sooner a young oyster can make a shell thick 

 enough to resist such attacks the better, not only for 

 the oyster but for us also ; for once past this dangerous 

 4 



