118 JELLY-FISH, STAR-FISII, AND SEA-URCHINS. 



ing between the bell and the manubrium. Never- 

 theless, in many cases, irritating any part of the 

 band a I has the effect of causing the manubrium 

 to perform the active random motions previously 

 described. In such cases, however, it is observable 

 that the further away from the manubiium the 

 stimulus is applied, the less active is the response 

 of this organ. In very many instances, indeed, the 

 manubrium altogether fails to respond to stimuli 

 applied at more than a certain distance from itself. 

 For example, referring to Fig. 23, the manubrium 

 might actively respond to irritation of any point 

 in the division d, e, /, g, w^hile to irritation of any 

 point in the division /, g, h, i its responses would 

 be weaker, and to irritation of any point in //, i, j, k, 

 they would be very uncertain or altogether absent. 

 Hence in this form of section we have reached 

 about the limit of tolerance of which the non- radial 

 connections between the bell and manubrium are 

 capable. 



Another interesting fact brought out by this form 

 of section is, that the radial tubes are tracts of 

 comparatively high irritability as regards the manu- 

 brium ; for the certainty and vigour with which 

 the manubrium responds to a stimidus aoplied at 

 one of the severed radial tubes, /, g, or h, i, or j, k, 

 contrast strongly with the uncertainty and feeble- 

 ness with which it often responds to stimuli applied 

 between any of these tubes. Indeed, it frequently 

 happens that a specimen which will not respond 

 at all to a stimulus applied between two radial 

 tubes, will respond at once to a stimulus applied 



