BIVALVE MOLLUSCA. 377 
i ; 
Fig. 170.—Groups of Oysters of different ages attached to a block of wood. 
merchandise ; that is to say, it is in a state to be sent to the parks 
for preservation and feeding. In Fig. 171 we see a group of oysters,* 
* We give this illustration as representing the comparative size of the oysters 
at different ages ; but it is necessary to state that the specimens were artificially 
