XI 



PHYLUM MOLLUSCA 



275 



The nervous system is formed on a type quite different 

 from anything we have yet met with. On each side of the 

 gullet is a small cerebro-pleural ganglion (Fig. 150, c. pi. gn,\ 

 united with its fellow of the opposite side by a nerve-cord 

 the cerebral commissure passing above the gullet. Each 



art 2 



FIG. 152. Diagram of the circulatory system of Anodonta. Vessels containing 

 aerated blood red, non-aerated blue. of. br. v. afferent branchial veins ; ao- 

 aorta ; art.i, artery to mantle; art. 2, artery to body generally; au. auricle; 

 ef. br. t>. efferent branchial veins ; nph. v. nephridial veins ; pc. pericardium ; 

 v. ventricle ; v. c. vena cava. The arrows show the direction of the current. 



cerebro-pleural ganglion also gives off a cord, the cerebro- 

 pedal connective, which passes downwards and backwards to a 

 pedal ganglion (pd. gn.) situated at the junction of the 

 visceral mass with the foot : the two pedal ganglia are so 

 closely united as to form a single bilobed mass. From each 

 cerebro-pleural ganglion there further proceeds a long 



T 2 



