62 



COMPARATIVE ANATOMY 



senting the outer and inner lamellae are also united from place 

 to place by hollow outgrowths called inter-lamellar junctions, 



Fig. 14 



A . Diagram of the hinder face of a single gill filament oiMytilus edulis. 

 dl, descending limb of the filament ; asl, ascending limb ; ij\ inter- 

 lamellar junctions ; ci, ciliated junctions. B. Vertical section 

 through the body of Anodonta cyg-nea in the posterior region of 

 the foot. Pc, pericardial cavity ; V, ventricle; Au, auricles; R, 

 rectum \yrapped round by the ventricle ; VC, vena cava below the 

 pericardial floor ; Ur, ureter or non-glandular part, and gl, glan- 

 dular part of the excretory organ ; Si.fi, supra-branchial passages ; 

 OG, outer gill lamella ; IG, inner gill lamella ; yj/, mantle ; M\ 

 thickened muscular border of the mantle : /, intestine, of which 

 there are several coils in the foot. (B, original ; A after Holman 

 Peck.) 



which clearly correspond to the vertical partitions connecting 

 the outer and inner laminse in Anodonta (fig. 13, A). By 



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