XXI. 



OYSTERS. 



303 



often spoken of as the " beard." And in addition to this 

 fleshy beard there is also a kind of fleshy moustache, con- 



OYSTER. 



The right valve of the shell has been removed, and the right mantle- 

 lobe has been cut away along the dark lines which take their origin in the 

 neighbourhood of the confluence of the mantle-lobes (c.m.L), where the 

 two lobes are fused or united above the hinder edge of the gills (g.g.). 

 m.l.m. is the margin of the left lobe of the mantle. Below the hinge (h.) 

 the hood has been slit open, c.e.h. marking its cut edge folded back. The 

 mouth (ra.) with its "moustache," formed by the right (r.p.} and left (Lp.) 

 labial pulps, is thus displayed. The alimentary canal terminates at the 

 vent (v.) in the posterior chamber (p.ch.) (the supra-branchial chamber of 

 anatomists), which runs along the inner edge of the gills (g.g.}. The 

 arrow passes into the part of the chamber which has not been opened up. 

 ad.m. is the adductor muscle for closing the valves of the shell, ch.h. is 

 the chamber in which lies the heart, dimly visible through its semi- 

 transparent walls. 



sisting of two flaps on each side arising from the corners 

 of the wide slit-like mouth, which must be sought in front, 



