120 Our Food Mollusks 



accidentally present in the water (Figures 25 to 28), the 

 practice arose of purposely throwing objects on the bot- 

 tom to capture them. Naturally, old oyster shells ac- 

 cumulated on the shore suggested themselves as collectors, 

 and from that day to this, they have been the most gen- 

 erally used of collectors in America. 



Shells are cheap, and are to be had near oyster grounds. 

 Firm bottoms are usually selected for spat collecting, but 

 the young are sometimes secured on soft ground. This 

 is possible because the shells settle with their concave or 

 inner surfaces uppermost. The edges of the shells are 

 thus held above the mud, and even when the deadly silt is 

 sufficient to kill those attached to the upper faces, others 

 continue to exist on the under side of their margins. 



The great disadvantage in using the oyster shell for a 

 collector is that it is so large that a great many young 

 may attach to it, and so tough that it cannot be broken to 

 separate them. A large cluster may thus arise on a single 

 shell, the individuals of which, from crowding, die or be- 

 come elongated; and it is only after they have attained a 

 considerable size that the cluster can be broken apart 

 without great loss. But, on the whole, the oyster shell 

 has proved to be the best of available collectors on the At- 

 lantic coast. 



There are some shells that are superior to it in many 

 respects. Such are the thin, brittle shells of the scallop, 

 the mussel, and the small " jingle shells " found on some 

 beaches. If these are used where currents are not strong 

 enough to bear them away, oysters that grow on them 

 will break them into bits as soon as pressure is developed 

 from crowding. In quiet waters these shells are ideal 

 collectors because of this fact that the clusters formed 

 on them will separate automatically without handling ; but 



