XII 



PHYLUM MOLLUSCA 



639 



together to the sides of the visceral mass a little below the origin 

 of the mantle : the inner lamella of the inner gill is also attached 

 to the visceral mass in front (A), but is free further back (B). The 

 gills are longer than the visceral mass, and project behind it, below 



rcb 



ink 



ic.. 530. Anodonta cygnca. Three transverse sections, av. auricle ; 1>1. urinary bladder ; 

 < .<'. ;//. external gill ; //. foot ; /. /. ./'. inter-lamellar junction ; int. intestine ; ii>t. <jl. internal 

 i.: ill ; M. kidney ; k. o. Keber's organ ; !(/. ligament; m. mantle ; p. ad. posterior adductor; 

 pc. pericardium ; ret. rectum ; s. Ijr. c. supra-branchial chamber ; sh. shell ; ty. typhlosole ; 

 r. gn. visceral ganglion. (After Howes, slightly altered.) 



;he posterior adductor (C), as far as the posterior edge of the 

 mantle : in this region the inner lamellae of the right and left 

 inner gills are united with one another, and the dorsal edges 

 of all four gills constitute a horizontal partition between the pallial 

 cavity below and the exhalant chamber or cloaca above. Owing 



