THE ORIGIN OF NERVES. 285 



ments in the margin of the bell. If we cut off the rim of the 

 bell with its tentacles and "marginal bodies," the animal 

 becomes completely paralysed ; whilst the detached and 

 separated rim will continue, under favourable circumstances, 

 to move and contract even for days after its severance from 

 the body of which it once formed part. 



That the nervous acts of a medusa are infinitely superior 

 in respect of their definite manner of working to those of 

 the amoeba may be demonstrated by one or two very 

 simple experiments. If, in certain species of medusae, such 

 as Tiaropsis (Fig. 50), we irritate any part of the swimming- 



FIG. 50. Tiaropsis indicans. 



bell the central mouth or polypite will move over towards 

 the irritated point, and indicate accurately the exact seat 

 of the irritation. Now, such an observation seems to prove, 

 without any reasonable shadow of doubt, that the im- 

 pressions made upon the body of the animal have been 

 conveyed to the central polypite; not irregularly or in- 

 definitely, but in definite lines or tracts, which, to use 

 Spencer's term, we may name " lines of discharge." And 

 that these lines communicate with other lines or tracts, just 

 as nerves interlace in higher animals, appears to be equally 

 clearly proved by the results which follow the formation 

 of a transverse or cross cut in the body of the jelly-fish. 

 If such an incision (/>, c) be made, and if thereafter the 



