184 THE MICROSCOPE AND ITS LESSONS. 



minifera become embedded in the network of the sponge, 

 and there they remain, as the grain of sand does which 

 forms the nucleus of the pearl which is found in the shell 

 of the oyster. And thus, with myriads of grains of sand 



Foramin'fera, r rom the sponge of commerce. 



which likewise find an entrance, with the water, into the 

 body of the sponge, sand and foraminifera become 

 commingled. 



My friend already referred to says, " I recently pre- 

 pared about thirty pounds of ' sponge-sand,' obtaining, as 



