1875 EXPBEIMENTS ON MEDUSA 17 



ordinary circumstances, exclusively due. This deduc- 

 tion was confirmed by the behaviour of the severed 

 thread-like portion of the margin, which continued 

 its rhythmical contractions quite unimpaired by its 

 severance from the main organism, the latter remain- 

 ing perfectly motionless. In the ' covered-eyed ' 

 forms Eomanes found that excision of the margin 

 of the umbrella, or rather excision of the sense organs 

 or marginal bodies, produced paralysis ; in this case, 

 the paralysis was of a temporary character, as in the 

 great majority of cases contractions were resumed 

 after a variable period. From this series of experi- 

 ments he was led to believe that in the ' covered- 

 eyed ' MedusaB the margin is the principal, but not 

 the exclusive, seat of spontaneity, there being other 

 locomotor centres scattered throughout the general 

 contractile tissue of the swimming bell. 



Having demonstrated the existence of a central 

 nervous system capable of originating impulses, 

 Eomanes had yet to prove the identity of this nervous 

 tissue of the Medusae with that of nervous tissues in 

 general : therefore, he next proceeded to test whether 

 it was also capable of responding to external stimu- 

 lation by light, heat, electricity, &c. 



As regards appreciation of light, he was able to 

 prove conclusively for at least two species of the 

 ' naked-eyed ' forms that as long as their marginal 

 bodies remained intact they would always respond to 

 luminous stimulation, and would crowd along a beam 

 of light cast through a darkened bell jar in which 

 they were swimming ; if their marginal bodies were 

 removed, they remained indifferent to light. With 

 regard to the ' covered-eyed ' forms, he obtained 

 sufficient evidence to induce him to believe they 

 possessed a visual sense localised in their marginal 

 sense organs. 



The effects of electrical stimulation agreed in all 



