EXPERIMENTS ON ARTHROPODS 113 



an operation in the thalamus opticus begins to move 

 spontaneously again if the optic lobes and the pars 

 commissuralis of the medulla are removed. 



In Limulus an anterior and a posterior nerve 

 originate from every ganglion of the ventral chain. 

 It was interesting to determine whether these nerves 

 have functional differences like those of the anterior 

 and posterior roots of the spinal cord of Vertebrates. 

 It has been maintained that Arthropods are Verte- 

 brates that walk on their backs. Faivre has stated 

 that there is not only a separation of the motor and 

 sensory roots in Arthropods, corresponding to Bell's 

 law, but that also in Arthropods, in contrast with Ver- 

 tebrates, the ventral side of the ganglia is sensory, the 

 dorsal motor. Now this is not true of the nerve- 

 roots which start from the ganglia in Limulus. If the 

 posterior nerve be severed and its peripheral stump 

 stimulated, we get inspiratory movements of the half 

 of the gills to which this nerve goes. All the other 

 gills are unaffected. Hence this nerve contains 

 motor fibres. If the ventral stump be stimulated, 

 the whole animal becomes much excited. From this 

 we see that the posterior nerve also contains sensory 

 fibres. If the anterior nerve be severed, stimulation 

 of the peripheral stump has no effect. Stimulation 

 of the central stump excites the entire animal. Hence 

 the anterior nerve is purely sensory. Limulus is 

 better adapted for deciding this question than the 

 smaller Arthropods. The conditions in the latter are 

 probably the same as in the former, for Vulpian (4) 



