244 



Papers from the Department of Marine Biology. 



Table 19. 



is a progressive shrinkage in the diameter, due to starvation and 

 decrease in volume, tension of the regenerating tissue after re- 

 moval of the rhopalia, and in- 

 creased tonus of the musculature 

 (sometimes transforming the disk 

 into a cup-shape) . This decrease 

 in the diameter is associated with 

 increase in revolutions per second, 

 but agitation decreases the revo- 

 lutions per second. It is there- 

 fore necessary to make the deter- 

 minations under the same con- 

 ditions for strictly comparative 

 results. The determinations in 

 table 19 were rough, but serve to 

 indicate the general features. 



A comparison of these experi- 

 ments with those on the actual 

 velocity of the wave shows the 

 circumference of the potential 

 pace-making circuit to be about 1.8 times the diameter. 



If the contraction-wave is stopped by pressure and after a rest of 

 some minutes or hours is started again, it is slower than just before 

 stopping, but if it is started again as quickly as possible after stoppage 

 the rate is the same. This effect of a rest may be associated with 

 nutrition or recovery from fatigue, since the amplitude of the contrac- 

 tion-wave is greater in the rested umbrella, although the number of 

 revolutions per second is decreased. Whether the actual rate of 

 propagation is changed would be difficult to determine. It seems evi- 

 dent that the wave of nerve-impulse precedes the wave of muscular 

 contraction. The contraction of the muscle must stretch the adjacent 

 regions, and hence stretch the region through which the nerve-impulse 

 is passing, thus increasing the distance traveled in one revolution and 

 decreasing the revolutions per second. When the amplitude of con- 

 traction is increased, the stretching of the nerves is increased and the 

 revolutions per second are decreased, but whether this can account for 

 the total decrease has not been determined. The speeding-up of the 

 revolutions per second after the trapped wave is started is at first 

 more abrupt and later more gradual, and is associated with both de- 

 crease in amplitude of contraction and decrease in diameter of the 

 umbrella, due to starvation and contraction of scar-tissue. 



Evidently a change in the number of revolutions per second of the 

 trapped wave or the amplitude of the contractions would cause an error 

 in the determination of the effect of O2 concentration on metaboHsm, 

 and in order to estimate the limits of such errors the relative metabo- 



