140 



FIRST LESSONS IN ZOOLOGY 



shell halves, one valve being hollowed out to receive the 

 body, while the other is nearly flat. It is attached to the 

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

 When first hatched the young oyster (fig. lOI ) swims 

 frcel}' about b}' 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 develop- 

 ment. The }-oung o}'sters when first attached are called 

 "spat"; when a little older this "spat," now called 



Fig. 102. — riiolas sp., a mullusc, burruwint; in sanclstoiie. (riiotngraph by 

 C. II. Sm'jw; perniissiuu <'f A)in-r. Soc. Civil Engineers.) 



"seed," may be transplanted to new beds, ^\-hich are 

 stocked ill this wa\-. In fact some licds have constantly 

 tn be thus restocked, the \'oung o}-stcrs produced on them 

 not finding good places to attach themseh'cs, and so 

 swimming awa\'. Sometimes pieces of slate, pottery, 

 etc., are strewed about the o_\-stcr-l)cds to serve as " col- 

 lectors " —that is, as places for the attachment of the 

 young o)-stcrs. The extent of the acreage of the Ameri- 

 can o\-ster-beds is larger than that of any other countr\'. 

 'II1C Baltimore o\-ster-beds (Jii the Cliesapeake River and 

 its tributaries cover 3000 acres, and produce an annual 

 crr>p of 25,000,000 bushels. 



