Nervous System of the Razor-shell Clam 323 



the ganglia themselves. With these gangha the operation is very 

 simple as they are connected by a long narrow commissure that 

 is distinctly visible throughout its length. With the commissure 

 cut it vv^as found that certain activities were delayed or otherwise 

 interfered with. Stimulating either ganglion apparently caused 

 complete contraction of the foot. The same result was also 

 obtained when the cerebral ganglion that was not to be stimulated 

 was removed previous to the experiment, or, as already noted, if 

 both cerebro-pedal connectives were cut and the cut end of one 

 of them w^as stimulated. These experiments again show that to 

 cause the action of the foot it is only necessary to stimulate one 

 pedal ganglion, which sets up the necessary association impulses. 

 If both cerebral ganglia had been left connected with the pedal 

 or visceral ganglia, although separated from each other, it would 

 have been possible that stimulation of one resulted in the stimula- 

 tion of the other through the pedal or visceral gangha. Similar 

 experiments were tried to determine the effect upon the visceral 

 ganglia when one cerebral was stimulated after the cerebral com- 

 missure had been cut. The siphons and posterior mantle margins 

 of both sides always contracted completely, even though the un- 

 stimulated cerebral ganghon was separated by cutting connectives, 

 or was removed. The results were thus similar to those obtained 

 for the pedal ganglia. 



With the cerebral commissure cut and the two sides of the collar 

 separated to guard against a possible transfer of impulses through 

 the anterior pallial nerves, although no evidence could be found 

 that such transfer of impulses could be made when the nerves were 

 intact, moderate stimulation of one side of the collar caused only 

 the contraction of the same side of the collar with imperfect con- 

 tractions of the anterior adductor muscle and possibly sHght con- 

 tractions of the anterior foot muscle of the same side, with the 

 usual retraction of the foot siphons, etc. Strong and continued 

 stimulation however caused contraction of the other side of the 

 collar as well. Evidently the impulses that affected the cere- 

 bral ganghon that has control of this side of the collar, must have 

 passed by way of either the pedal or the visceral gangha. Experi- 

 ment indicated that the impulses can be transmitted either way but 



