POISONS. 247 



tion cease after the extreme margin of the bell has 

 been removed. For some reason or another the 

 integrity of the margin here seems to be necessary 

 forexciting the manubrium to perform its movements 

 of localization. It is clear that this reason must 

 either be that the margin contains the nerve-centres 

 which preside over these localizing movements of 

 the manubrium, or, much more probably, that it 

 contains some peripheral nervous structures which 

 are alone capable of transmitting to the manubrium 

 a stimulus adequate to evoke the movements of 

 localization. In its unmutilated state this Medusa 

 is at intervals perpetually applying the extremity 

 of its manubrium to one part or another of the 

 margin of the bell, the part of the margin touched 

 always bending in to meet the approaching ex- 

 tremity of the manubrium. In some cases it can 

 be seen that the object of this co-ordinated move- 

 ment is to allow the extremity of the manubrium — 

 i.e. the mouth of the animal — to pick off a small 

 particle of food that has become entangled in the 

 marginal tentacles. It is therefore not improbable 

 that in all cases this is the object of such move- 

 ments, although in most cases the particle which 

 is caught by the tentacles is too small to be seen 

 with the naked eye. As it is thus no doubt a 

 matter of great importance in the economy of the 

 Medusa that its marginal tentacles should be very 

 sensitive to contact with minute particles, so that a 

 very slight stimulus applied to them should start 

 the co-ordinated movements of localizati(<n, it is not 

 surprising that the tentacular rim should present 



