i8 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



Our first question is : Is the spontaneous locomo- 

 tion of the Medusae, or the rhythmical contraction of 

 their swimming-bell, a function of the ganglion-cells ? 



Romanes found 

 - that if the margin of 

 the bell of a Hydro- 

 medusa (6, Fig. 3) be 

 cut off, the rhythmical 

 contraction of the 

 centre of the bell (a, 

 Fig. 3) ceases, while 



FIG. 2. DIAGRAM OF THE BELL OF AURELIA t\\Q margin b which 



AURITA, WITH EIGHT SENSE ORGANS. 



(After ciaus.) contains the nerve- 



ring, continues to ex- 

 ecute rhythmical contractions (2). The wound does 

 not even cause a decrease in the number or in the 

 strength of the marginal contractions. The exper- 

 iment has been repeated by other authors with the 

 same result. Any sort of wound can be made in 

 the umbrella without disturbing the rhythmical con- 

 tractions so long as the nerve-ring remains intact. 

 Thus Romanes concluded that these rhythmical con- 

 tractions of Hydromedusse originate in the nerve- 

 ring or its ganglia. I have found recently that this 

 whole problem is not so much a morphological problem 

 as a problem of physical chemistry. The osmotic 

 pressure of the sea-water is about equal to that of a 

 -| n NaCl solution. I found that if the centre of a 

 swimming-bell be put into a -| n NaCl or |- n NaBr 

 solution it goes on beating rhythmically. But if a 



