434 
bulletin of the bureau of fisheries. 
portion of this structure, since they do not seem to be closely associated with muscles. 
The other nerves which belong to the visceral ganglia are the following: A pair of large 
nerves which penetrate the adductor muscles (fig. n, 6 ), a large pair to the posterior 
portions of the gills (fig. n, 7), and a pair of very small nerves (fig. n, 8 ), which are 
distributed to the kidneys. I have been unable to find the nerves to the anterior part 
of the gills. These nerves, however, arise from the visceral ganglia, as can be proven by 
experimental methods. If the gills are isolated from the cerebral and pedal ganglia by 
cutting all possible connectives, they will still contract when the posterior part of the 
mantle is stimulated. The anterior part of the gills will contract under these conditions, 
even after the large nerve to the posterior part of these organs has been cut. It is there- 
fore evident that the nerve supply of the gills comes entirely from the visceral ganglia. 
The circumpallial nerve lies near the edge of the mantle, to which it gives off numer- 
ous small nerves. (Fig. 12, cp.) It runs entirely around the mantle, passing across the 
mid line at either end, and thus forms a complete ring. Although it seems to contain 
Fig. 12. — Drawing to show distribution of mantle nerves, eg, Cerebral ganglion; pg, pedal ganglion; cc, 
cerebral connective; c, cerebro visceral connective, cp, circumpallial connective; 1, 2, and 3, mantle 
nerves from the visceral ganglion; 4, mantle nerves from the cerebral ganglion; ot, otocyst. 
many nuclei it has no motor nerve cells. If the nerves from the cerebral and visceral 
ganglia are cut the mantle is paralyzed. The neuclei which might be mistaken for nerve 
cells probably belong to the nerve sheath. 
A number of experiments were performed to determine which parts of the body are 
supplied with nerves from each ganglion. The experimental and anatomical evidence 
agree and there seems to be little if any overlapping. Each ganglion seems to supply its 
own definite regions of the body. The visceral ganglion controls the posterior part of 
the mantle, posterior adductor muscle, gills, mantle gland, and kidneys. The cerebral 
ganglia control the anterior part of the mantle, the palps, anterior adductor, and anterior 
retractor muscles. The cerebral and pedal ganglia together control the foot, posterior 
retractor muscle, and byssus. The nerves to the viscera and heart were not discovered. 
A more complete account of the experimental study of the nervous system of this form 
is given in a paper published in the Johns Hopkins University circular for June, 1909 (4). 
The most interesting feature of this work was the discovery of reflexes. For example, 
