FRESH-WATER MUSSEL. 287 



along which a bristle has been drawn as passing. The glandular por- 

 tions of the two nephridia communicate freely with each other, as do 

 also the excretory sacs in this species. 



/. Orifice of the duct of the generative gland. This orifice is concealed 

 in Anodonta, though not in Unto, by the attachment of the inner gill- 

 lamina to the visceral mass. See V. Baer, Meckel's Archiv. 1830, 

 p. 318. 



