FIELD BOOK OF PONDS AND STREAMS 



Fig. 261. — A mussel, with the shell and mantle 

 of its left side removed to show the body lying with- 

 in the mantle cavity: i, mantle flap of right side; 2, 

 foot; 3, gills of left side; 4., triangular lip hiding the 

 mouth; 5, anterior and 6, posterior adductor mus- 

 cles; 7, incurrent and 8, excurrent siphons which 

 have been cut open; 9, cut edge of mantle of left 

 side. 



particles with it. The foot is the fleshy process by which 

 mussels plough their way through the mud. Mussels are 

 often said to "lie on the bottom with their tongues out". 

 These "tongues" are their feet. The mussel's whole body, 

 gills, foot, and other organs lie within the mantle cavity. 



\arooa ^>oucn 



Fig. 262. — I, A female mussel, with the left 

 valve of shell and mantle removed to show the 

 brood pouch; 2, a larval mussal or glochidium much 

 enlarged. 



Eggs and young. — The small mussels (SphcBridce) are her- 

 maphrodites but in the large ones eggs are produced by one in- 



318 



