1875 EXPEEIMENTS ON MEDUSAE 17 



up the much-debated question by saying that 

 'no nervous system had yet been discovered in 

 Medusae.' 



Microscopically, it had already been shown that 

 in some forms of Medusae there are present certain 

 fine fibres running along the margin of the swimming 

 bell, from their appearance said to be nerves, but 

 in no case had it been shown tbat they functioned 

 as such. Thus it was to solve this question, whether 

 or not a nervous system, known to be present in all 

 animals higher in the zoological scale, makes its 

 first appearance in the Medusae, that Mr. Eomanes 

 entered upon a long series of physiological experi- 

 ments, first on the group of small ' naked-eyed ' 

 Medusae, and then on the larger ' covered-eyed ' form, 

 the latter division containing the common jelly-fish. 

 These names, ' naked-eyed ' and ' covered-eyed,' are 

 given to the two groups on account of a difference in 

 their sense organs, which are situated on the margin 

 of the umbrella or swimming bell, and are protected 

 by a hood of gelatinous matter in the ' covered-eyed ' 

 forms, so called in contradistinction to the ' naked- 

 eyed ' group, where the hood is absent. 



Romanes first carefully observed the movements 

 of the Medusae, which, it will be remembered, are 

 effected by the dilatation and contraction of the 

 entire swimming bell, and he found that if, in the 

 ' naked-eyed ' group, the extreme margin of this 

 swimming bell be excised, immediate, total, and per- 

 manent paralysis of the whole organ took place. This 

 result was obtained with every species of this group 

 which he examined ; he therefore concluded that in 

 the margin of all these forms there is situated a 

 localised system of centres of spontaneity, having 

 for one of its functions the origination of impulses to 



c 



