258 FUNCTIONS AND INSTINCTS. 



tranquillity of the water in these tanks, generate 

 a vast number of seminiform germes, which 

 entering the shells of the oysters when they 

 open them to take their food so it is stated 

 stain them with their own hue. 



They have other enemies besides man : who- 

 ever has observed their shells will often see them 

 quite covered with a small kind of sea-acorns. 1 

 Tt is related also that certain crabs get into their 

 shells, first introducing a piece of stone to hinder 

 them from shutting, but this is probably fabu- 

 lous ; they may, however, when the oysters 

 open their shells to receive the sea- water, enter 

 them as they do those of the muscles and the 

 wing-shell, either for protection or for the sake 

 of food. It is observed that the oyster defends 

 itself against intrusive enemies by squirting 

 upon them with force water kept in reserve in 

 their shells ; they keep out those that attempt to 

 pierce their shells to get at them, by thickening 

 them in the part attacked. 



I shall next give some account of a bivalve 

 that has interested mankind from a very early 

 period of history, on account of the valuable gem 

 that it produces, and which is frequently men- 

 tioned in Holy Scripture. The Supreme Being, 

 in his goodness and attention to the wants and 

 tastes of his principal creature, has not neglected 

 to furnish him with various articles for ornament 



1 Bo/ami*, &e. 



