62 JELLY-FISH, STAR-FISII, AND SEA-URCHINS. 



Medusae by drawing off the water in wliich tliey 

 floated with a siphon, while at the same time I 

 substituted w^ater of a different temperature from 

 that which I thus abstracted. In this way, without 

 modifying any of the other conditions to which the 

 animals were exposed, I was able to observe the 

 efiects of changing the temperature alone. 



With regard to the effect of temperature on the 

 latent period of stimulation, the following table, 

 setting forth the results of one among several 

 experiments, explains itself 



Period of latent stimulation of the deganglio- 

 nated tissues of Aurelia aurita as affected by tem- 

 perature : — 



Temperature of water (Fahr.). 



70- 



35° 



20° 



Period of latent stimulation. 



^ second 

 ^ second 

 I second 

 ^ second 



In the case of each observation, several shocks 

 were administered before the latent period was 

 taken, in order to decrease this period to its 

 TiiinimuTn by the staircase action. When this is 

 not done, the latent period at 20° may be as long 

 as 1 J seconds ; but soon after this irritability 

 disappears. 



The extraordinary sluggishness of the latent 

 period at very low temperatures is fully equalled 

 by the no less extraordinary sluggishness of the 

 contraction. 



