NATURAL HISTORY OF SLIPPEK-LIMPET. 443 



(1) To keep up the food supply of the oysters. 



(2) To destroy, besides the oysters' active enemies, as many as 

 possible of those animals which take the same food as oysters, as, 

 for example, the slipper-limpet, mussels, most tube-dwelling worms, 

 other animals similar to the oyster, barnacles, and all the different 

 kinds of sea-squirts. 



It should be borne in mind that sea-squirts are nearly as common 

 on some grounds as Crepidula, and that they are just as likely to take 

 away the oyster's food as is Crepidula. 



