292 Adjustment to Conditions of Aquatic Life 



tion appears to do little harm to the fishes. The 

 cysts are soon grown, emptied and sloughed off, leaving 

 no scar. And a few fishes, such as the sheepshead 

 which is host for many mussels, appear to reap an 

 indirect return, in that their food consists mainly of 

 these same mussels when well grown. 



It may be noted in passing that one little European 

 fish, the bitterling, has turned tables on the mussels. 

 It possesses a long ovipositor by means of which it 

 inserts its own eggs into the gill cavity of a mussel, 

 where they are incubated. 





'ii 



