32 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



FIG. 8. DIAGRAM FOR EXPLAIN- 

 ING THE LOCALISING REFLEX IN 

 MEDUSAE. (See text.) 



is impossible. Romanes concludes from this that 

 there are radial lines of differentiated tissue pass- 

 ing through all parts of the bell and that it is 

 their function to transmit impressions to the manu- 



brium. He assumes that 

 this tissue is of a nervous 

 character. I believe that 

 the whole phenomenon can 

 be explained without the as- 

 sumption of a special differ- 

 entiation of nervous tissue 

 in radial directions. It seems 

 to me that the following as- 

 sumption is possible : Every localised stimulus leads 

 to an increase in the muscular tension on all sides, 

 which is most intense near the stimulated spot. Now 

 if we decompose each of the lines of increase of tension 

 (aa' ab' ac' ad' ae 1 , Fig. 8) radiating from the stimul- 

 ated spot, into a meridional component aa' dd' bb' , etc., 

 and an equatorial component, it is evident that the lat- 

 ter can have no influence on the manubrium. Only 

 the meridional components can have an influence, and 

 of these the one passing through the stimulated spot is 

 the largest. This fact must necessarily cause a bend- 

 ing of the manubrium toward the stimulated spot. 

 It also shows why an incision parallel to the mar- 

 gin of the umbrella makes an exact localisation impos- 

 sible and only allows uncertain movements towards 

 the stimulated quadrant. 



I hardly believe that the mechanisms for the 



