VII 



269 



FIG. in. 



The three chief types of Mollusc. A, a Gasteropod (Helix) ; B, a Siphonopod (Sepia) ; C, z 

 Pelecypod (Anodonta). Ai, Anterior adductor muscle ; A 2, posterior adductor ; a, anus ; e, eye 

 F, foot ; /, fin ; g.o, genital opening ; h, head ; i.g, inner gill ; l.p, labial palp ; M, mantle-flap 

 m, mouth ; o.g, outer gill ; p.a, pulmonary aperture ; r.a, retractile arm ; v.h, visceral hump. 



