OYSTERS AND METHODS OF OYSTER-CULTURE. 291 



indepeudeiitly of its fellows or in conjunction with them. As shown 

 in ulate xvi, the starfish feeding upon oysters or other lamellibranchs 

 arches itself over the nibs or lips of the mollusk so that some of its arms 

 are on one side and some on the other. In this position a large number 

 of the sucker feet are attached to each valve, and when they contract 

 a stress is produced in opposite directions and opposed to the force of 

 the adductor muscle wliich tends to keep the valves of the oyster 

 closed. Dr. Schiemenz has shown by actual measurement that in this 

 manner there is exerted a force sui^cient to overcome any resistance 

 which the oyster may ofler. It is eventually tired out by the persist- 

 ence of its enemy, its shell is forced ojien, the stomach of the starfish 

 is inserted, and within a few hours the valves oul}^ remain. 



Another annoying and frequently very destructive enemy of the 

 oyster is the boring-sponge, CUona sulphurea. It differs from the 

 enemies before enumerated in that it consumes the shell and not the 

 soft parts of the unfortunate oyster. The young sponge lives in galleries 

 excavated in the substance of either dead or living shells which are 

 soon reduced to a honey-combed condition, when they may be crumbled 

 to powder between the fingers. When they attack a living oyster, 

 as tlie galleries penetrate the inner face of the shell, an irritation of 

 the mantle is j^roduced, causing an increased amount of shell deposit 

 at that point. If the inside of such a shell be examined it will be found 

 to be covered with blister-like shell deposits, sealing up the openings to 

 the galleries, and many curious distortions follow from the destruction 

 of the hinge area and the portion of the shell to which the adductor 

 muscle is attached. Although the oyster itself is not attacked, yet it 

 becomes poor, thin, and watery and often dies from the exhaustion 

 induced by the constant effort to keep its shell intact. 



The older specimens of the boring-sponge are large, dense, yellow 

 masses, often G or 7 inches in diameter and usually inclosing the shells, 

 etc., to which they were originally attached. All stages intermediate 

 between those described can usually be found upon infested oyster- 

 beds. The older, more massive forms often suffocate the oyster through 

 the deuseness of their growth. 



In addition to the various forms already enumerated there is a large 

 population upon the oyster-beds which is not injurious. This, of course, 

 includes many of the minute food Ibrms, together with some of the fishes 

 and crabs. The latter, at least on the Atlantic coast, can not be 

 regarded as very destructive, but on the contrary they serve as scav- 

 engers, removing dead matter trom the beds when it might otherwise 

 become foul and fatal to the oysters. It will be seen that the popula- 

 tion of the oyster-beds is large and extremely complex. The social 

 relations of the various forms are exceedingly intricate and have, in 

 the course of evolution, become nicely adjusted in a system of reciprocity. 

 The law of the oyster beds is "give and take," each of a large number 

 of organisms giving something for the general welfare and taking what 

 it needs for its own well being. 



