The Oyster. 53 



better for the market on muddy bottoms, where there are 

 great quantities of tiny plants for their food. So when 

 they are half grown, the oystermen take them up and 

 " plant" them on the mud in some warm bay or at the 

 mouth of a river, where they are left for a year or two. 

 But thpy never dig in the mud, and so need neither foot 

 nor siphon. 



I should think the currents of water would get mixed 

 if there isn't any siphon. 



Is there any place where the edges of the mantle are 

 joined together ? 



Yes, at the bar. 



Then what is the use of the bar ? 



To separate the two currents of water. 



One current flows in nnder the convex border of the mantle, 

 pagsing over and throngh the gilla, and carrying food to the month, 

 the other flowa ont on the opposite side of the bar, as indicated by 

 the arrows in Fig. 1. 



As in the case of the clam and oyster, so with other mollagks the 

 presence or absence of the foot and siphon is a anre gnide to the 

 habits of the animal. 



