MOLLUSCA 573 



The gonad discharges into the right kidney as in the Diotocardia 

 among Gasteropoda. 



Fig. 391. Diagram of the structure of Z)ew^a/m?«. Ahered from Naef. Head 

 and foot stippled, an. anus; buc. buccal mass, with radula; ce.g. cerebral 

 ganglion; eta. captacula; dig.gl. digestive gland; F. foot; gon. gonad, com- 

 municating with the cavity of the left kidney {k.) ; M. mouth ; yyia. mantle ; 

 max. mantle cavity; pl.g. pleural ganglion; ped.g. pedal ganglion; sh. shell; 

 St. stomach; vis.g. visceral ganglion. The mollusc is represented buried in 

 sand, except for the perforated narrow end, through which both the inhalant 

 and exhalant currents (shown by arrows) flow. 



Class LAMELLIBRANCHIATA 



Mollusca in which typically the body is bilaterally symmetrical, much 

 compressed from side to side and completely enveloped by the mantle 

 which is divided into two equal lobes ; each lobe secretes a shell valve, 

 the two valves being joined dorsally by a ligament and hhige and closed 

 ventrally by the contraction of one or two transverse adductor muscles 



