MOLLUSCA: THE MOLLUSCS 249 



some solid object and grows truly oyster-like. Much care 

 has to be taken in cultivating oysters to furnish proper 

 conditions for growth and development. The young 

 oysters when first attached are called ' * spat ' ' ; when a 

 little older this "spat," now called "seed," may be 

 transplanted to new beds, which are stocked in this way. 

 In fact some beds have constantly to be thus restocked, 

 the young oysters produced on them not finding good 

 places to attach themselves, and so swimming away. 

 Sometimes pieces of slate, pottery, etc., are strewed about 

 the oyster-beds to serve as ' ' collectors, ' ' that is, as 

 places for the attachment of the young oysters. The 



FIG. 105. Dactylus sp.. a mollusc, excavating granite. (Photograph by 

 C. H. Snow; permission of Amer. Soc. Civil Engineers.) 



extent of the acreage of the American oyster-beds is 

 larger than that .of any other country. "The Baltimore 

 oyster-beds on the Chesapeake River and its tributaries 

 cover 3,000 acres, and produce an annual crop of 25,000, - 

 ooo bushels." 



The " pearl-oyster " is not a true oyster, that is, not a 

 member of the family to which the edible oysters belong, 



