XI 



PHYLUM MOLLUSCA 



285 



shows that the departure from symmetry is very marked. 

 The left side of the body has become very much more 

 strongly developed than the right, and is drawn out into 

 a spirally-twisted prominence the visceral spiral enclosing 



FIG. 160. Shell of Triton nodiferus. Natural size. 



the liver and other organs. The anal aperture, instead of 

 being median and posterior, is situated on the right side, 

 and in front of it on the same side is the reproductive 

 aperture. 



