132 NATURE’S CRAFTSMEN 
lodge in the creature’s body, and then a miracle 
begins-” 
“ Oh, I know, Uncle John,” Ruth again in¬ 
terrupted excitedly. “ It’s an oyster! Not the 
miracle,—that’s a pearl. But it’s an oyster you 
are describing.” 
“ No, it isn’t,” assured Uncle John, stoutly. 
“ Of course not,” affirmed Tommy. “No one 
ever saw an oyster down by our boat-house! And 
Uncle John said he saw this creature’s trail there 
this morning! Subside, chicken.” 
Ruth obligingly clapped her hands over her 
mouth, but it was plain from her dancing eyes 
that she had another guess coming. 
“ As soon as the little creature feels the irrita¬ 
tion of the sand,” continued Uncle John, “ she 
throws over it a thin, milky substance called 
nacre. Thus penned in, the sand and the nacre 
together at length turn into a beautiful pearl. 
And it is to get the pearls that thousands of these 
little creatures’ homes are taken from our rivers, 
lakes, and ponds each year. Indeed, along the 
Mississippi River more than one thousand people 
are at this work all the summer long. . . . 
Now, what is it? ” 
“ A clam! 39 shouted Ruth. 
“ Yes, a clam,” agreed Uncle John, “ or 
more properly speaking a mussel. Clams are 
really creatures of the sea. They differ con- 
