EX PERI MEN TS ON AR THRO PODS 1 1 1 



movements (2). It was necessary to make these exper- 

 iments on young or new-born Vertebrates, as on them 

 the effect of the shock does not last so long. If one 

 succeeds in keeping these animals alive by introducing 

 artificial respiration until the effect of the shock result- 

 ing from the operation has passed off, spontaneous 

 respiration begins again. I consider it possible that, 

 if we could keep an adult Vertebrate alive without the 

 nceud vital for some time, the respiratory motions 

 would be resumed again. But why does respiration 

 stop temporarily after the isolation of the segmental re- 

 spiratory ganglia from the higher parts of the central 

 nervous system ? An answer to this question would be 

 in part an explanation of the mystery of the shock- 

 effects. It might be possible that something has to be 

 supplied constantly by certain nerve-elements in the 

 subcesophageal ganglion or the medulla to the seg- 

 mental respiratory ganglia, which enables the latter to 

 be active automatically. In destroying the nceud vital 

 we perhaps destroy the pathway along which these 

 constant impulses are carried to the segmental re- 

 spiratory ganglia in the spinal cord. But where do 

 these impulses come from and what is their character ? 

 In watching the respiratory motions of a Limulus, I 

 received the impression that the operculum always 

 moves first, and that the respiratory motions of the 

 lower segments follow successively. In the lower 

 Vertebrates, e. g. the frog, we have a mouth respir- 

 ation, whose segmental ganglia are situated in the 

 medulla. Likewise the segmental ganglia for the 



