MOLLUSCA 



67 



The greater part of the alimentary canal is embedded 

 in other organic systems, and it is distinctly seen only as it 

 passes through the pericardial cavity. 



Coelom. The pericardial cavity is the main part of the 

 coelom or body cavity, and is restricted to a region of the 

 body dorsally in front of the posterior adductor. The intestine 



Pericardial cavity 

 Ventricle 

 Intestine 

 Auricle 



Vena cava Ureter 

 Nerve cord 



External gill 

 . Internal gill 



Foot 



Mantle 



Line of attachment 

 to sheU 



FIG. 31. Anodonta. Transverse section in region of heart. 

 The shell is removed. 



and the heart may be easily seen through the thin wall. In 

 front it receives the openings of Keber's gland or the peri- 

 cardial gland, which is excretory and spreads on each side of 

 the front of the pericardial cavity. It communicates with 

 the exhalent system by a pair of coelomiducts or kidneys, 

 the organ of Bojanus. The internal openings of the coelomi- 

 ducts are situated at the extreme anterior end of the cavity, 

 and the external openings on each side opposite to them on 

 the body wall in the cavity of the inner gill. If the gill cavity 

 be opened in this region two small apertures will be disclosed, 

 just at the place where the dark part of the kidneys ends 



