4 Art. 3.— N. Yatsu: 



If all the rhopalia be extracted, the animal instantly ceases 

 to pulsate and remains still on the bottom of the vessel. In a 

 few cases the jellyfish thus operated resumed pulsation for a short 

 length of time, and even tried to swim up. But they did not 

 seem to have strength enough to pull up the relaxed tentacles. In 

 the above cases the cutting off of four pedal ganglia did not stop 

 pulsating. Very seldom do the medusae deprived of all the rliopalia 

 lift themselves up and swim for a short distance. It may be added 

 that by pinching the tentacles (even at the distal end) weak pulsa- 

 tions may be aroused in the medusae destitute of all the rhopalia. 



It is evident that from the above experiments as well as 

 from those of previous authors, that the pulsation center is localiz- 

 ed in the rhopalium. Now the question naturally arises as to what 

 part of the organ sends out stimuli to the subumbrellar muscles 

 to cause pulsation. In dealing with the problem the concretion 

 can a priori be left out of consideration, 

 since it has nothing to do with nervous 

 function and moreover its extraction from ' •• . 



all the rhopalia does not in the least impair ^^,__U/ ■ y 



the swimming activity of the medusa (Berger /^^ÉT^:^^ V 

 ^00 p. 8). To decide the question the Wi^^ ^"^^^>^ 

 following simple experiments were per- vfll^^H .1 



formed. Three rhopalia were pulled off, and ^^ J^K ]^ 



from the remaining one only the eye part 7 



together with the concretion was cut off. 



Fig. 1. 



Pulsation continued without any impairment. 



Only when the part near the stalk was excised, the jellyfish 

 became motionless (Fig. 1). From these experiments it may be 

 concluded that the pulsation center is located in the part next to 

 the stalk. And I think that this conclusion is born out by the 



