106 



THE FRESHWATER MUSSEL. 



a. The pericardial cavity is very much larger and has 

 thinner walls than in the previous section : it is 

 triangular in shape. 



Fia. 28 Anodonta cygnea. Transverse section of the animal passing 



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

 the ieart is dotted, (a. si. m.) 



A, shell. AXr, left auricle. B, ligament. BC, branchial cavity. F, 

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

 of the right side. LM, left mantle-lobe. OG, left outer gill. PC, peri- 

 cardial cavity. B, cavity of rectum. EG, genital gland, ovary, or testis. 

 BM, edge of right mantle-lobe. SC, supra-branchial canal of right outer 

 gill, T^typhloBole. TJ, left ureter. V, wall of ventricle. V, cavity of ven- 

 tricle. 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 iind 

 the body is the slit through which the branchial cavity communicates with 

 the supi'a-brauchial canal of the inner gill. Y, the right cerebro-visceral con- 

 nective. 



