STRUCTDRE OF 1AMELLIBRANCH1ATA. 



393 



formed ; this occupies a large part of the cavity of the shell 

 during the breeding season. Close to this is the posterior adduc- 

 tor muscle ; by which, with the aid of the anterior muscle 



/Anterior 

 \Ganglia 



Intestine . 



Stomach 



Gills 



Mantle 



i Posterior 

 1 Muscle 



Anus 



Respiratory Tubes 

 FIG. 586. ANATOMY OF AN ACEPHALOUS MOLLUSK. 



situated near the mouth, the valves can be drawn together with 

 considerable force. The intestinal tube is seen to terminate near 

 the opening at the posterior extremity of the shell, in one of the 

 respiratory tubes, which discharges its contents, and serves for 

 the exit of the respiratory current. 



