30 



Papers from the Marine Biological Laboratory at Tortugas. 



much slower than that to which the nervous network and the underlying 

 muscles can respond, and thus the danger of muscular fatigue is avoided. 



As has been pointed out by Romanes (1885), Bethe (1903), and Harvey 

 (191 1), there must be some mechanism of adjustment by virtue of which 

 the wave travels at a faster rate around the rim than at points nearer the 

 center of the subumbrella, the rate being directly proportional to the 

 length of the radius of the zone of pulsation. 



In order to determine the average rate of transmission of the pulsation- 

 impulse by the nervous network, eight separate rings were cut, one from each 

 of eight Cassiopea xamachana. These rings were each 90 mm. in outside 

 diameter, 67 mm. in inside diameter, and 11.5 mm. wide. Thus the mean 

 diameter of each ring was 78.5 mm. and its mean circumference 247 mm. 



Table i. 



* This ring exhibits pulsus alternans. For an explanation of this phenomenon, see 

 G. A. Mines, 1912, Proc. Cambridge Philosophical Society, vol. 16, p. 617. 



The results obtained from the kymograph record, figure i, are stated 

 in table i, which shows the rate of nerve transmission, in millimeters per 

 second, determined in natural sea-water, ranging in temperature from 28° 

 to 30.45° C. 



These 8 medusae ranged from 97 to 115 mm. in diameter, and their 

 pulsation- waves traveled at rates varying from 384 to 481 mm. per second, 

 the average being 440 at an average temperature of 28.9° C. In these 

 experiments, the rate of transmission bears no relation to the size of the 

 medusa. 



All experiments show that, as in other invertebrates, strong stimuli 

 travel faster than weak ones. Thus should a ring stop, we can not start 

 it again and continue the same series of experiments with it, for the 

 new stimulus is almost certain to differ in strength from the former one; 

 or, if all care be taken to make the successive electrical stimuli as nearly 

 as possible identical in strength, they will be received differently by the 

 tissue and the resulting pulsation-waves will differ in rate. Thus a ring 

 must remain in pulsation throughout the entire series of experiments that 

 one performs upon it or no conclusions can be drawn respecting the relative 

 rates of its pulsation-stimulus in the various solutions. 



