ANATOMY OF THE CLAM. 

 A B 



65 



Fia. 73. — A, Mt/a arenaria with its siphons extended ; iu 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; M, adductor muscle; 

 the hgament represented by the dark mass; C, section of Mya, showing the 

 position of the spring to open the shell; L, ligament; D. transverse spctica 

 of Unio (after Brooks); ab, visceral mass; a, anricles: v, ventricle; i, intes- 

 tine; (, glandular part of kidney; z, non-glandular part of kidney; y, sinus 

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



