40) JELLY-FISH, STAR-FISH, AND SEA-URCHINS, 
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 Sarsize are 
more active in the light than they are in the dark, 
the comparative duration of the quiescent stages 
being 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 vm situ, 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 monograph already 
alluded to, ‘‘Die Deutung der Sinnesorgane niederer Thiere 
gehort ohne Zweifel zu den schwierigsten Objecten der vergleic- 
henden Physiologie und ist der gréssten Unsicherheit unterworfen. 
Wir sind gewohnt, die von den Wirbelthieren gewonnenen 
