VII 



MOLL USCARESPIRA TOR Y ORGANS 



85 



bilateral symmetry of the body, such as the Lamellibranchia, the 

 Cephalopoda, and a point of great importance also in the primitive 



fcr 



FIG. 81. Ctenidia of various Molluscs (after Ray Lankester). A, Chiton ; B, Sepia ; C, 

 Fissurella ; D, Nucula ; E, Paludina. ft, Longitudinal branchial muscle ; abv, afferent branchial 

 vessel ; ebv, efferent branchial vessel (branchial vein) ; gl, paired lamellae (leaflets) of the feathered 

 gill ; in D : d, position of the axis ; a, inner ; b and c, outer rows of branchial lamella: ; in E : i, 

 rectum ; br, branchial filaments ; a, anus. 



Gastropoda, the Zeugobranchia. In the latter, however, the left ctenidium 

 was originally the right and vice versa, but this will be dealt with more 

 in detail later. 



