E. W. BERGER ON THE CUBOMEDUS^E. 15 



amount of labor necessary to force the water out of two openings 

 instead of one, namely, past the velarium. Just how much this 

 observation bears upon Romanes' theory of rhythmic contraction, 

 that the rhythm is due to an alternate exhaustion and recovery of 

 the contractile tissue, as opposed to the ganglionic theory of rhythm 

 of physiologists, one does not wish to speculate much. Yet, I feel 

 that the observation rather supports this theory. The tissue having 

 to do less work, would become less exhausted at each contraction and 

 require less time for recovery and hence have a more rapid rhythm. 

 I here sum up Romanes 1 theory in a few words. The ganglia 

 liberate a constant and comparatively weak stimulus, one perhaps 

 about minimal. This stimulus sets off the contractile tissue ; but as 

 the tissue contracts and becomes exhausted the constant stimulus 

 becomes, in relation to it, sub-minimal, and it does not contract 

 again until it has recovered and the stimulus is again strong enough 

 to set it off. The ganglionic theory of rhythmic contraction supposes 

 that the ganglia liberate stimuli to the contractile tissue at successive 

 intervals. Romanes had this theory suggested to him by the rhythmic 

 contractions he succeeded in obtaining by subjecting deganglionated 

 bells to a continuous but weak faradic stimulus, or by placing them 

 into weakly acidulated water, or into 5 per cent, glycerine. Romanes 

 claims that his theory better explains muscular tonus and the 

 contraction of involuntary muscle. He does not, however, hold this 

 theory to the exclusion of the ganglionic theory, since only too often 

 does he speak in terms of the latter. He further brings in his 

 support the fact that the frog's tongue, in which no ganglia have 

 been demonstrated, can be made to contract rhythmically when 

 subjected to a weak and continuous stimulus. He also calls attention 

 to the rhythmic contractions seen in the Protozoa, the snail's heart, 

 etc. Finally, physiologists are much inclined to explain the rhythmic 

 contraction of the heart and other involuntary muscles, in part, at 

 least, as due to a property of the contractile tissue. 



Margin, Radial Ganglia, Nerve Experiments 18, 21-23, 30. 

 Complete removal of the margin did not stop pulsation ; but the 

 removal of the radial ganglia stopped it permanently. While this 

 experiment seems to have been tried only once, yet, taking into 

 consideration the results of other operations, it would seem that the 

 principal centers of spontaneity reside in these ganglia. (It should 



