PHYLUM MOLLUSCA 



273 



tubes all open dorsally into a suprabranchial chamber, 

 continuous posteriorly with the cloaca and thus opening on 

 the exterior by the exhalant siphon. 



The physiological importance of 

 obvious. By the action of their cilia 

 which sets in through the inhalant 



T 



the gills will now be 



a current is produced 



siphon into the pallia! 



