3l6 Gil man A. D 



rew 



Ipn. Dorsally and anteriorly a nerve is continued to the corre- 

 sponding anterior foot muscle, Fig. 2, afn. Anteriorly a large 

 nerve that soon branches starts forward. A portion of the first 

 branch of this nerve bends ventrally to the margin of the mantle 

 lobe and is continued posteriorly as the circum-paUial nerve, Fig. 

 2, cpn. The remainder of this first branch is continued forward 

 toward the collar. The second branch from this large anterior 

 nerve, aan, supplies the anterior adductor muscle. It is not always 

 given off^ at exactly the same point in difi^erent specimens, and it 

 sometimes happens, as in the case of the specimen shown by Fig. 

 2, that the origins of the nerves on the two sides are not symmetrical. 

 The examination of serial sections and physiological experiments 

 both indicate that these are the only nerves that supply this large 

 muscle. The remainder of the large anterior nerve is continued 

 anteriorly and sends numerous branches to the collar reigon of the 

 mantle. The nerves of the two sides are continuous in front of 

 the anterior adductor muscle so a complete connection between 

 the two cerebral ganglia is formed, just as the circum-paUial nerves 

 connect the cerebral and visceral ganglia of their respective sides. 

 It may be well to state here that, while such anatomical connec- 

 tions undoubtedly exist between these ganglia, repeated experi-- 

 ments have failed to show the possibihty of sending a nervous 

 impulse from one ganglion to another by either of these connec- 

 tions. Possibly neurones from the two ganglia overlap in their dis- 

 tribution so there may be more complete coordination between 

 portions that work together. 



Upon cutting the inner lamellae of the inner gills where they are 

 joined together, and pushing them to their respective sides, the 

 visceral ganglia, Fig. 2, vg^ are immediately seen. They lie just 

 anterior to the posterior adductor muscle, sometimes, as in the 

 specimen shown in Fig. 2, with their posterior ends overlapping the 

 anterior border of the muscle. The visceral ganglia are closely 

 fused, so there is only a shght constriction between them. The 

 commissural fibers are distinctly visible in sections but ganglion 

 cells cover them entirely. As already indicated each visceral 

 ganglion is joined to the corresponding cerebral ganglion by a 

 connective, Figs, i and 2, cvc, that runs along the side of the body. 



