ABERRANT ANIMALS-THE MOLLUSKS AND ECHINODERMS 259 



cavity, forces the blood through the circu- 

 latory system of the clam (Figs. 12-7, 12-8). 

 The ventricle, which is joined by two later- 

 ally situated auricles, pumps the blood for- 

 ward into an anterior aorta, supplying the 

 muscular foot and viscera, and posteriorly, 

 through the posterior aorta, supplying the 

 rectum and the mantle. Blood from those 

 parts of the body supplied by the aortas, 

 with the exception of the mantle, is re- 

 turned through a vein to the nephridia, or 



to absorption through diffusion. This is 

 particularly true in the region of the foot 

 where blood sinuses are numerous. 



Two U-shaped kidneys lie ventral to the 

 pericardial cavity (Figs. 12-6, 12-7). These 

 function in the removal of wastes from the 

 blood and other fluid of the pericardial cav- 

 ity. Each is a tubular organ, folded upon 

 itself and divided into glandular and 

 bladder-like parts. A ciliated opening from 

 the pericardial chamber into the glandu- 



visccral ganglia 



cerebnoyisceral 

 connective 



cerebropleurol 

 ganglia 



— cerebral 

 commissure 



cerebropeddi 

 coonectiye 



pedal gonglici 



dorsal view 



Fig. 12-9. Anterio-dorsal schematic drawing of the nervous system of the clam. 



kidneys, for the elimination of waste prod- 

 ucts. It then moves to the gills to pick up 

 oxygen and eliminate carbon dioxide. Oxy- 

 genated blood is returned from the gills on 

 each side of the clam to the corresponding 

 auricle. The mantle also returns oxygenated 

 blood to the auricles. Unlike the circulatory 

 system of some other animals, some of the 

 arteries and veins of the clam are not 

 joined by capillaries, but end in sinuses, 

 vsdthout cellular Hning. Food and oxygen 

 carried directly to these sinuses can pass into 

 intercellular spaces and are not restricted 



lar portion drains this region, while the 

 bladder region opens into the path of the 

 excurrent water, thus carrying wastes out 

 of the body. 



Three pairs of ganglia and their connect- 

 ing nerve cords constitute the nervous sys- 

 tem of the fresh-water clam (Fig. 12-9). 

 Each pair of ganglia controls the body 

 region in which it is located: the anterior 

 or cerebropleural ganglia on either side of 

 the mouth; the pedal ganglia in the foot; 

 and the posterior or visceral ganglia ven- 

 tral to the posterior adductor muscle. Each 



