SECTION OF NAKED-EYED MEDUSZ. 105 
occurring in the manubrium, this cannot properly 
be regarded as a case of reflex action. But now 
the converse of the above statement is likewise true, 
viz. that when any part of the manubrium is irri- 
tated, the bell responds; and it is in this that the 
unequivocal evidence of reflex action consists, for 
while the sympathy of the manubrium with the 
bell is not in the least impaired by removing the 
marginal ganglia of the latter, the sympathy of 
the bell with the manubrium is by this operation 
entirely destroyed. 
We have thus very excellent demonstration of 
the occurrence of reflex action in the Meduse. 
Further experiments show that the reflex action 
occurs, not between the marginal ganglia and every 
part of the manubrium, but only between the 
marginal ganglia and the point of the bell from 
which the manubrium is suspended—it being only 
the pull which is exerted upon this point when 
the manubrium contracts that acts as a stimulus 
to the marginal ganglia. But the high degree of 
sensitiveness shown by the marginal ganglia to the 
smallest amount of traction of this kind is quite as 
remarkable as their lack of sensitiveness to dis- 
turbances going on in the manubrium. 
Turning now to the physiological evidence of 
the distribution of nerves in Sarsia, when one of 
the four tentacles is very gently irritated, it alone 
contracts. If the irritation be slightly stronger, all 
the four tentacles, and likewise the manubrium, 
contract. If one of the four tentacles be irritated 
still more strongly, the bell responds with one or 
