50 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
with all its constituent parts as distinct from one 
another as they were at starting from the proximal 
end of the strip. 
Period of Latency, and Summation of Stimulz. 
I shall now give an account of my experiments 
in the period of latency and the summation of 
stimuli. To do this, I must first describe the method 
which I adopted in order to obtain a graphic record 
of the movements which were given in response to 
the stimuli supplied. As Aurelia aurita is the only 
species on which I have experimented in this con- 
nection, my remarks under this heading wiil be 
confined to it alone. 
The method by which I determined the latent 
period in the case of this species was as follows. 
A basin containing the Medusa was filled to its 
brim with sea-water, and placed close beside a 
smoked cylinder, which, while it lay in a horizontal 
position, could be rotated at a known rate. The 
Aurelia* was placed with its concave aspect upper- 
most, and an inch or two below the surface of the 
water. The animal was held firmly in this position 
by means of a pair of compasses thrust through it 
and forced into a piece of wood, which was fastened 
to the bottom of the basin. The legs of the com- 
* It may here be stated that in all the experiments on stimu- 
lation subsequently to be detailed, there is no difference to be 
observed between the behaviour of an entire swimming organ 
deprived of its ganglia, and that of a portion of any size which 
may be separated from it. 
