The Pond Mussel. 65 



with the earthworm, or with a vertebrated animal. The heart 

 consists of a thick-walled ventricle, which is coiled round the 

 intestine, with which communicate two thin-walled auricles, 

 and from which arise two main arteries, one anterior and one 

 posterior. The ccelom thus conforms to the coelomic cavity 

 of other animals (of. earthworm, frog), in that (i) it contains 

 various viscera — in the present case the heart and a part of the 

 alimentary canal only ; (2) it communicates with the exterior 



HEART 



INTESTINE 

 CILOM 

 AUR 

 NEPHRIDIUM 



Fig. 30.— Diagrammatic transverse section of Anodon. (Partly after T. J. Parker.) 

 INT, intestine in foot ; AUR, auricle. 



by means of secretory tubes, the organs of Bojanus, which are 

 the kidneys; (3) the third character of the ccelom is not 

 apparent in the mussel, for the gonads are removed from 

 the coelomic wall, and have come to lie in the thickness of 

 the body, whence special ducts convey their products to the 

 exterior. 



The organs of Bojanus, or kidneys (Fig. 29 neph, and Fig. 

 30), already referred to, are the precise equivalents of the 

 nephridia of the earthworm. Each is essentially a tube, 

 opening, on the one hand, by an orifice into the pericardium 

 (= ccelom), and by another orifice on to the exterior of the 



F 



