THE CLAM AND OTHER BIVALVED SHELL-FISH 57 



FIG. 59. A, the clam with its siphon extended; in its natural position in the 

 mud. head downwards. B, Unio. or fresh- water mussel; transverse section of 

 the shell, showing the position of the spring opening- the shell; in, adductor 

 muscle. C, clam: I, ligament. D. transverse view of animal of Unio (after 

 Brooks); at>, abdomen or visceral mass; a, auricles; v, ventricle; i, intestine: 

 t, glandular part of kidney; z, non-glandular part of kidney; y, sinus venosus; 

 ig, inner, eg, outer, gills; m, mantle. 



