POISONS. 947 
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— 
ze. 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 localization, it is not 
surprising that the tentacular rim should present 
