58 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 



in response to the second, tliird, or even fourth 

 shock of the series. This fact conclusively proves 

 that the staircase effect, at any rate at its com- 

 mencement, depends on the process of stimulation 

 as distinguished from that of contraction ; for it is 

 obvious that the latter process cannot play any 

 part in thus constructing what we may term the 

 invisible steps of a staircase. 



To answer the second of the above questions, I 

 placed an Aurelia with its concave suriace upper- 

 most, and removed seven of its lithocysts ; I then 

 observed the spontaneous discharge of the remain- 

 ing one, and found it to be conspicuous enough that, 

 after the occurrence of one of the natural pauses (if' 

 this were of sufficient duration), the first contraction 

 was feeble, the next stronger, the next still stronger, 

 and so on, till the maximum was attained. This 

 natural staircase action admits of being very prettily 

 shown in another way. If a tolerably large Aurelia 

 is cut into a spiral strip of small width and great 

 length, and if all the lithocysts are removed except 

 one at one end of the strip, it may be observed that, 

 after the occurrence of a natural pause, the first 

 discharge only penetrates perhaps about a quarter 

 of the length of the strip, the next discharge pene- 

 trates a little further, the next further, and so on, 

 till finally the contraction waves pass from end to 

 end. On now removing the ganglion, waiting a 

 few minutes, and then stimulating with successive 

 induction shocks, the same progressive penetration 

 is observable as that which previously took place 

 with the ganglionic stimulation. Lastly, the 



