14 



Papers from the Marine Biological Laboratory at Tortugas. 



Table 2 gives the mean rates of pulsation derived from the study of 7 

 separate medusae (with marginal sense-organs intact) at various tempera- 

 tures, the rates stated in the table being the arithmetical mean of the 

 observed rates. Thus if 3 medusae each pulsated at the rate of 3 per 

 minute, and if 4 others each pulsated at the rate of 10 per minute, the 

 average rate of pulsation would be 7. 



Table 2. 



16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 



Degrees Centigrade 



Fig. 4, illustrating Table 2. 



The observations recorded in table 2 are plotted in figure 4, wherein it 

 appears that the rate at which the motor-centers engender stimuli declines 

 if the medusa be cooled or heated from 33. In both heating or cooling 

 the loss of rate is slight at first, but constantly augments as we continue to 

 cool or heat the animal. In fact, the loss of rate is about proportional to 



