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 Suniraation of Stimuli 



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 will 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, wdiich, 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 an}' size which 

 may be separated from i- . 



