o O 



But it is in our own country that the Unio 

 reaches its greatest size and perfection 

 and where we have more species than 

 the rest of the world combined. The 

 streams flowing into the Atlantic Ocean 

 along our Eastern sea-board, contain but 

 few of these shells which are mostly small 

 and inferior, but throughout the Mississippi 

 valley, from the great lakes to the Gulf 

 of Mexico, the rivers contain these mussels 

 in great abundance, many of them noted 

 for their great size and magnificent coloring. 



Origin of the Pearl 



The old theory that the pearl is caused 

 by a grain of sand becoming embedded in 

 the mantle or nacre-secreting portion of the 

 mollusk and covered with layers of pearly 

 matter, has generally been abandoned. 

 Scientific research has shown that the origin 

 of the pearl is a minute parasite which 

 bores its way into the fleshy portion of the 

 animal which, in self protection, encloses it 

 in pearly matter to stop its further progress. 

 This parasite is usually walled out and 

 fastened down to the interior of the shell 

 before it works its way deep enough into 

 the mantle, to make a nucleus for a pearl. 

 But on rare occasions, as a pearl is an 

 abnormal growth, the parasite is enclosed 

 in a fold or pocket in the fleshy mantle, 



10 15 20 30 



Sizes of Pearls in Grains 



