EXPERMIENTS ON MED US^E 33 



analogous reflex in a frog or turtle are of a more com- 

 plicated character. Nature works with very simple 

 tools. The tool employed in the reflex of localisa- 

 tion is the curvature produced by stimulation, con- 

 tact, for instance. We meet with this in its simplest 

 form in plants, in which the side that comes in con- 

 tact with a solid body becomes concave. Plants cer- 

 tainly possess no central nervous system containing 

 mysterious reflex structures. In their case, irritabil- 

 ity and conductibility suffice as an explanation. In 

 Medusae the method appears more complicated only 

 in so far as in them the contractile tissue is real mus- 

 cle-fibre. In the frog, the only further complication 

 is the fact that the conduction takes place through a 

 special kind of tissue namely, nerve-tissue. In its 

 first anlage, this central nervous system is of a very 

 simple segmental character. I believe that the cent- 

 ral nervous system preserves this simple character 

 better than any other tissue. The muscles undergo 

 considerable displacement during the development, 

 but the changes occurring in the central nervous sys- 

 tem by no means equal those occurring in the mus- 

 cular system. 



It seems thus possible to explain the above-men- 

 tioned phenomena of coordination in Medusae by 

 means of the simple facts of irritability and conduct- 

 ivity without attributing any other functions to the 

 ganglion-cell except those which occur in all conduct- 

 ing protoplasm. 



