120 
STRUCTURE OF CONCHIFERA OR BIVALVES. 
terminating near one of tlie canals or siphons, which also 
carries out the water that has been taken in through the other 
for the purposes of respiration. The figure also shows the 
large fleshy foot, by which this animal can move itself along 
Fig. 62. —Anatomy of Mactra. 
the ground, or bore into sand or mud. The heart and circu¬ 
lating system are less complete than in the Gasteropoda; but 
are far higher in character (as are most of the other parts 
