1 8 Our Food Mollusks 



was undoubtedly the condition of the distant ancestors 

 of the oysters, which were unattached. The habit of at- 

 tachment is of great value, for oysters are permanently 

 held in favorable localities above the soft mud of the bot- 

 toms, which might otherwise smother them. 



The primary function of the shell, of course, is protec- 

 tion. But in spite of its hardness and toughness, it some- 

 times fails. There is a mighty and unceasing struggle in 

 nature in which every organism strives to obtain necessary 

 nourishment, and at the same time to protect itself against 

 its enemies. The shells of bivalves have become strong, 

 but at the same time their enemies, which must in some 

 way obtain food or perish, have developed special organs 

 for crushing or penetrating them. The jaws of the drum- 

 fish of Atlantic and Gulf waters, for example, have be- 

 come so powerful that they are able to crush even the 

 strong shell of an oyster. But it is interesting to observe 

 that there is difficulty in doing this; for if the task were an 

 easy one, these fishes might be able to cause the extinction 

 of the race of oysters. Drumfish are able to dispose of 

 small oysters which the oyster culturist has separated and 

 scattered over the bottom to grow, but they experience so 

 great difficulty with oyster clusters on the natural beds, 

 that their mouths are often badly lacerated in their 

 desperate attempts to obtain food from them. The 

 sheepsheads, fish with jaws armed with large, hard 

 teeth, crush the relatively thin shells of young oysters. 

 Among the deadliest enemies of bivalves are some of 

 their own distant cousins, snail-like mollusks which pos- 

 sess, in the end of a proboscis, a rasping or boring organ 

 which slowly cuts through the hardest shell, and allows 

 the creature to feed on the pulpy tissues within. 



There is at least one phase of what is called the struggle 



