58 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
in response to the second, third, 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 surface 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 
