SECTION OF NAKED-EYED MEDUSA 105 



occurring in the manubrium, tliis 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 Medusae. 

 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 shoAvn 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 boll responds with one or 



