MOLLUSCA — PELECYPODS 



209 



The two lobes of the mantle are attached to the body dorsally, 

 and extending down over the sides, come closely together along 



Fig. 88. — The quahog, Venus mercenaria Linne, in position of feeding. (X f.) 

 Left valve separated from its mantle and muscles which are left lying in the right 

 valve, a.a., anterior adductor muscle and scar; a.r., anterior retractor muscle 

 (a portion of it is attached to the left valve) ; c.t., cardinal teeth ; e.s., excurrent 

 siphon ; i.s., incurrent siphon ; /., ligament ; /./., lateral teeth ; m.m., mantle 

 muscle; p.a., posterior adductor muscle and scar; p.l., pallial line (the scar left 

 by the mantle muscle); />./■., posterior retractor muscle and scar; ^.5., pallial 

 sinus (the scar left by the siphonal muscle) ; s.m., siphonal muscle. 



the ventral edge, thus inclosing the body of the animal as in a 

 sac. The siphons are merely projections of the mantle edge 

 united into muscular tubes. The lower is the incurrent or 

 branchial siphon ; it draws in water carrying food to the mouth 

 and oxygen to the gills. The upper is the excurrent or anal 

 siphon ; it discharges the waste products of the digestive system 

 and the water which has passed over the gills and has hence 

 become impure with the products of respiration. 



The organs of respiration are the gills and mantle. The gills 

 are two thin, curtain-like folds hanging free on each side of the 

 main body mass just beneath the mantle (Fig. 89, B). Each 



