54 JELLY-FISH, STAR-FISH, AND SKA-URCHINS. 



the cylinder being stationary during each response, 

 and rotated a short distance with the hand during 

 each interval of repose. 



The second tracing (Figs. 3 and 4) is a record of 

 the difference between the lengths of the latent 

 period, and also between the strengths of the con- 

 traction, in the case {a) of the first of such a series 

 of responses (Fig. 3), and (6) of the last of such a 

 series (Fig. 4). From these tracings it will be 

 manifest, without further comment, how surprising 

 is the effect of a series of stimuli; first, in aroiisliKj 

 the tissue, as it were, to increased activity, and, 

 second, in developing a state of expectancy. 



In accordance with the now customary termi- 

 nology, I shall call such a series of responses as are 

 given in Fig. 2a" staircase." Such a staircase has 

 a greater number of steps in it if caused by a weak 

 current (compare Figs. 2 and 5) ; and if the strength 

 of the current be suddenly increased after the 

 maximum level of a staircase has been reached by 

 using a feeble current, this level admits of being 

 s'ightly raised (see Fig. 5). Moreover, I lind that a 



