vii VICARIOUS NERVE-CENTRES 343 



as on other cells, a definite morphological character. Thus I 

 sought at first in vain for nerve- cells or brains in the 

 Scyphomedusse and could only discover the spots at which 

 the latter exist by the section-experiments above mentioned. 

 Such experiments afterwards completely confirmed my 

 description of the nervous system of Beroe. In both cases, 

 in Beroe as in the Scyphomedusse, the presence of a number 

 of nerve-cells, or of brains, could be recognised by the fact 

 that the parts in question, when separated from the rest of 

 the animal, alone, or at least in a pre-eminent degree, exhibited 

 life (movement). 



In Beroe I had found anatomically a gradual decrease in 

 the abundance of the nerve-cells from the closed end towards 

 the aperture. In power of movement the parts of the animal 

 when divided transversely exactly corresponded to this result. 

 The separated polar portion moved immediately after its 

 separation, in all respects like an entire uninjured animal. 

 The nearer to the aperture they were taken, the more the parts 

 were affected by separation, the longer time elapsed before they 

 showed traces of movement, the less were they capable of life. 



VICARIOUS NERVE-CENTRES. 



In the course of my section -experiments I observed a 

 remarkable fact which at present stands alone, and which has 

 an important bearing on my whole argument. 



The Medusa Aurelia aurita, when I had removed from it 

 all the primary nerve-centres, became completely motionless. 

 But after the animal thus mutilated had lain several days in 

 clean sea- water, it gradually commenced to exhibit movements 

 again : one day, movements at first trembling and irregular 

 appeared in the umbrella. These movements evidently 

 started from a definite spot which might be at any part 

 of the umbrella, and extended thence over the whole, 

 just as in the uninjured animal they proceed from 



