' STAR-FISH AND SEA-URCHINS. 289 
not invariably, induced again to expand. This is 
the only part of the whole organ the stimulation of 
which thus exerts an inhibitory influence on the 
contractile mechanism. If there is any functional 
purpose served by such relaxing influence of stimu- 
lating this particular part of the apparatus, we 
think it can only be as follows. When a portion of 
sea-weed brushes this particular part, it must be 
well below the tips of the mandibles, and therefore 
in a position where it, or some over-lying portion, 
may soon pass between the mandibles, if the latter 
are open; hence when touched in this place the 
mandibles, if closed, open to receive the sea-weed, 
should any part of it come within their cavity. 
Turning next to experiments in stimulation with 
reference to the spines, I may observe that we have 
found these organs to be, physiologically considered, 
highly remarkable and interesting, from the fact 
that they display co-ordinated action in a degree 
which entitles them to be regarded as a vast multi- 
tude of limbs. Thus, for instance, if an Echinus be 
taken out of the water and placed upon a table, it 
is no longer able to use its feet for the purpose of 
locomotion, as their suckers are only adapted to be 
used under water. Yet the animal is able to pro- 
gress slowly by means of the co-ordinated action of 
its spines, which are used to prop and push. the 
globe-like shell along in some continuous direction. 
If, while the animal is thus slowly progressing, a 
lighted match be held near it, facing the direction of 
advance, as soon as the animal comes close enough 
to feel the heat, all the spines begin to make the 
