TKANSVERSE SECTIONS 



99 



2. The visceral mass is cut across close to its posterior end, 

 and hence is much smaller than in the previous sec- 

 tion : it is occupied almost entirely by the generative 

 gland. 



BC 



RM 



FIG. 21. Anodonta cygnea. Transverse section of the animal passing 

 through the middle of the length of the ventricle. The cavity of 

 the heart is dotted. (A. M. M.) 



A, shell. AU, left auricle. B, ligament. BC, branchial cavity. 

 F,foot. I, intestine. IG, left inner gill. K, left kidney. KO, Keber's organ. 

 LM, left mantle-lobe. OG, left outer gill. PC, pericardial cavity. 

 B,, cavity of rectum. RG-, genital gland, ovary or testis. B,M, edge of right 

 mantle-lobe. SC, supra-branchial canal of right outer gill. T, typhlosole. 

 TJ, left ureter. V, wall of ventricle. V, cavity of ventricle. VC, vena cava. 

 W, supra-branchial canal of left inner gill. X, free upper edge of the inner 

 lamella of the right inner gill : between this edge and the body is the slit 

 through which the branchial cavity communicates with the supra-branchial 

 canal of the inner gill. Y, the right cerebro-osphradial connective. 



' H2 



