40 JELLY-FISH, STAR-FISH, AND SEA-UECHINS. 



the effect of the converse experiment just described 

 is rather that of inhibiting contractions ; for, if the 

 sunlight be suddenly shut off during the occurrence 

 of a swimming bout, it frequently happens that the 

 quiescent stage immediately sets in. Again, in 

 a general way, it is observable that Sarsise are 

 more active in the light than they are in the dark, 

 the comparative duration of the quiescent stages 

 beino- less in the former than in the latter case. 

 Light thus appears to act towards these animals as 

 a constant stimulus. Lastly, it may be stated that 

 when the marginal bodies of Sarsia are removed, 

 the swimming-bell, although still able to contract 

 spontaneously, no longer responds to luminous 

 stimulation of any kind or degree. But if only one 

 body be left in ^itu, or if the severed margin alone 

 be experimented upon, the same unfailing response 

 may be obtained to luminous stimulation as that 

 which is obtained from the entire animal. 



The fact last mentioned indicates that the mar- 

 ginal bodies are organs of special sense, adapted to 

 respond to luminous stimulation ; or, in more simple 

 words, that they perform the functions of sight. 

 Now it has long been thought more or less probable 

 that these marginal bodies are rudimentary or 

 incipient " eyes," but hitherto the supposition has 

 not been tested by experiment, and was therefore of 

 no more value than a guess.* The guess in this 



* As Professor Haeckel observes in his monofj^raph already 

 alluded to, '"Die Deutung der Sinnesorgane niederer Thiere 

 geliort ohne Zweifel zu den schwierigsten Obiecten der vergleic- 

 henden Pbysiologie nnd ist der grossten Unsicherbeit nnterworfen. 

 VVir Bind gewolint, die von den Wirbeltbieren gcwonnenen 



