ARTHROPODS AND MOLLUSCS 173 



and vegetation. Such mounds are the old feasting-places 

 of the early coast inhabitants, and the archaeologist often 

 finds in these "kitchen-middens," as they are called, various 

 relics of the early natives of the continent. 



Even more widely known than the clams are the oysters 

 (Ostrea virginiana), also members of this class of mol- 



FIG. 84. An Eastern oyster, Ostrea virginiana. (After photograph l>y 

 \V. H. C. Pynchon.) 



luscs. The oyster is carefully cultivated by man in many 

 countries. It has its two shells or two shell-halves dis- 

 similar, one valve being hollowed out to receive the body, 

 while the other is nearly flat. The oyster is attached to 

 the sea-bottom by the outside of the hollowed-out valve. 

 When first hatched the young oyster swims freely by means 

 of its cilia; after a few days it attaches itself to 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. 



