ANATOMY OF THE CLAM. 
65 
Fio. 72.— A, Mya arenaria with its siphons extended ; in its natural position in 
the mud head-end downwards; B, transversa section of the shell of Unio, 
showing the position of the spring opening the shell; if, adductor muscle; 
the ligament represented by the dark mass; C, section of Mya, showing the 
position of the spring to open the shell; i, ligament; Z), transverse section 
of Unio (after Brooks); ab, visceral mass; a, auricles; v, ventricle; ^, intes- 
tine; t, glandular part of kidney; non-glandular part of kidney; y, sinus 
venosus; ig^ inner, eg, outer, gills; m, mantle. 
