922 OYSTERS, AND ALL ABOUT THEM. 



stantly accumulating layers ; owing, however, to the 

 inclined position of the oyster, the tendency of the Pearl 

 is always to work downward through the tissues, towards 

 the hinge of the shell. Small Pearls often work their way 

 into the adductor muscle, and, owing to the fibres of this 

 part being coarse and close, it is almost impossible for a 

 large Pearl to penetrate them, but numbers of small ones 

 are frequently found here, bound together like a cluster of 

 grapes, showing that even within this muscle these Pearls 

 receive further accretions. In course of time such Pearls 

 as avoid passing into this muscle find their way downwards 

 to the lowest part of the oyster, and, according to their 

 position therein, may or may not find their way out of the 

 tissues of the oyster into the shell. 



Up to this time the Pearl has received regular layers 

 all over its surface, but rings and other marks of lesser 

 brightness frequently occur, the result probably of contact 

 with the coarser tissues of the ovster. For a short time 



j 



the Pearl is loose in the shell, and it falls into the same 

 category as a stone, or any other intruder. It is encircled 

 by the growing layer of shell, and proceeds on its down- 

 ward course through the shell, like an ordinary " blister," 

 (fi) the upper portion receiving further layers, until it is 

 hidden beneath the shell, which by degrees resumes its 

 natural shape. 



The shell is worn away from the outside at the same 

 rate that it is renewed within, so that in time the Pearl, 

 with its surrounding tomb, yields to the general dissolu- 



(h) An unnatural excrescence on the surface, often found in the 

 Meleagrince, and formed in the renovation of their shells by the habit of 

 the animals burying such intruders as they cannot rid themselves of. 

 Stones, mud, small shells, wood, and more especially layers of weed, 

 are thus found embedded in shells. 



