STAR-FISH AND SEA-UnCIIfNS. 289 



not invariably, induced again to expand. This is 

 the only pait 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 

 liojhted match be held near it, facinor the direction of 

 advance, as soon as the animal comes close enough 

 to feel tho heat, all the spines begin to make the 



