EXPERIMENTS ON MOLLUSKS 131 



article on Eledone is more exhaustive than Steiner's. 

 One of his observations, describing the extraordinarily 

 excited condition of an animal whose cerebral gan- 

 glion had been removed, is worthy of mention. " All 

 the reflexes seemed increased. When anyone ap- 

 proached the basin the Eledone that had undergone 

 this operation swam off, while the normal animals 

 remained quiet. There was an incessant play of 

 colors. During the second night, in spite of the pro- 

 tecting net, it escaped and died on the floor of the 

 laboratory." V. Uexkull concludes from this that there 

 are inhibitory centres in the cerebral ganglion. We 

 have seen that Bethe arrived at a similar conclusion 

 in regard to the supracesophageal ganglion of the 

 Arthropods. We have discussed this possibility in 

 connection with Maxwell's experiments on Nereis. 



The arm-nerves originate in the pedal ganglion. 

 But the latter is connected with the supracesophageal 

 ganglion directly by means of the anterior commis- 

 sures and indirectly by means of the posterior commis- 

 sures. Now it is of interest to know that the influence 

 which the anterior part of the supracesophageal gan- 

 glion exerts on the arm-movements when stimulated 

 is exactly the opposite of that exerted by the posterior 

 part ; if the entire supracesophageal mass between 

 both pairs of commissures be separated by a frontal 

 incision and both stumps be stimulated down deep, 

 where the central ganglia are located, according to v. 

 Uexkull, we obtain the following results : Stimulation 

 of the anterior stump causes the cup-like suckers to 



