EXPERIMENTS ON MEDUSAE 23 



eighty pulsations per minute- -/. e., about the period- 

 icity of the heart. 



Now, as regards the origin of the rhythmical activ- 

 ity of Medusae, of the heart, and of respiratory activity, 

 we can imagine that a constant fermentative produc- 

 tion of certain compounds in the automatically active 

 cell corresponds to the constant flow of alcohol in 

 Ouincke's experiment. These substances may be of 

 such a nature that they occasion spreading-phenomena 

 or some other physical change in the colloids of the 

 muscle. But a certain quantity of these substances 

 must be present before this change occurs, hence the 

 periodicity of the contractions. But whether it be a 

 constant fermentative production of some substance 

 or not, the ultimate constant cause for the production 

 is the heat or the intensity factor of the same the 

 temperature. It now can no longer surprise us that 

 Romanes found that the centre of an Acalepha is able 

 to beat rhythmically in normal sea-water if severed 

 from the margin. As long as we assume that the 

 ganglion-cells are the essential element in spontaneity, 

 this experience on Acalephse would be difficult to ex- 

 plain. As it is, we are only obliged to conclude that 

 in Acalephae there is less difference between the col- 

 loidal substances of the margin and centre than in 

 Hydromedusae. 



2. Not only the spontaneous character of locomo- 

 tions is commonly considered to be due to ganglion- 

 cells, but the coordinated character of these motions 

 as well. Let us see how far this notion is correct. 



