Papers from the Marine Biological Laboratory at Tortugas. 31 



On the other hand, temperature, purity of water, etc., being unchanged, 

 the rate remains nearly constant for any single stimulus. Thus Harvey 

 (191 1, p. 131) maintained such a ring in pulsation for 11 days at an average 

 velocity of 774 mm. per second. I once had a ring which remained in 

 pulsation for 6 days, the wave traveling from 200 to 206 times per minute 

 around the ring. The rings live for two or more weeks and exhibit abortive 

 efforts at regeneration, but being without means of obtaining food they 

 gradually decline in size and die. 



'j\l\NV\N\i\i 



-If/^c, Wo.) 30° V5 C 



%%' 



I\|\j\l\j\j\JW\^ 



\l\f\j\j\PKf\f\f\p<Af\\\\vy\f\f\f\r^^ 



6 i«?.**i 



Z9.7 



% t•l•n^«. each ?0 'irs' out-iae, 

 and 67 -mm . tn&icie eltameter. 



Fig. I. 



These pulsating rings are usually almost machine-like in their uni- 

 formity of rate under unchanged environmental conditions; but while the 

 rate of nerve-conduction remains quite constant, the muscles become 

 fatigued and thus the amplitude of pulsation steadily declines, becoming 

 much reduced at the end of a few days. Thus the muscles fatigue more 

 readily than do the nerves. 



Kymographic records enable us to study not only the rate, but the form 

 of the pulsation-wave, and this is important; for in order that comparisons 

 may be made it is necessary that the character of the wave should not change 

 throughout the series of tests to which the ring may be subjected in the 

 course of any one set of experiments. 



For example, the series of lines on the record (fig. 2), which were obtained 

 from a single medusa, can not safely be compared one with another and the 

 record is therefore worthless, on account of the tendency of the pulsation- 

 stimulus to break up into two waves, the one following the other at the 

 same or at different rates as in lines i and 3 from the top of the figure; or, 

 the wave may break up into a complex series of strong and weak wavelets 

 due to spontaneous excitement, as in line 5. 



