EEFLEX MOVEMENTS OF ARTICULATA. 357 



the ganglia of the trunk, when separated from the head, are 

 often very remarkable, and seem at first sight to indicate 

 sensation and a guiding will; but, when they are carefully 

 studied, it is found that striking differences are to be detected, 

 by which their nature is found to be simply reflex, a certain 

 stimulus or irritation producing a certain movement, without 

 any choice or guidance on the part of the animal, and pro- 

 bably without its consciousness. As there are no animals in 

 which these reflex movements are more remarkable than they 

 are in Centipedes and Insects, we shall pause to dwell upon 

 them here in more detail. 



443. If the head of a Centipede be cut off whilst the animal 

 is in motion, the body will continue to move onwards by the 

 action of the legs ; and the same will take place if the body 

 be divided into several distinct portions. After these actions 

 have come to an end, they may be excited again by irritating 

 any part of the nervous centres, or the cut extremity of the 

 nervous cord. The body is moved forwards by the regular 

 and successive action of the legs, as in the natural state ; but 

 its movements are always forwards, never backwards ; and are 

 only directed to one side when the direct movement is 

 checked by an interposed obstacle. There is not the slightest 

 indication of consciousness, either in direction of object, or in 

 avoidance of danger. If the body be opposed in its progress, 

 by an obstacle not more than one half its own height^ it 

 mounts over it and moves directly onwards, as in a natural 

 state ; but if the height of the obstacle be equal to its own, its 

 progress is arrested, and the cut extremity of the body 

 remains opposed to it, with the legs still moving. If, again, 

 the nervous cord of a Centipede be divided in the middle of 

 the trunk, so that the hinder legs are cut off from connexion 

 with the cephalic ganglia, they will continue to move, but not 

 in harmony with those in the fore part of the body, being 

 completely withdrawn from any .control on the part of the 

 animal, though still capable of performing reflex movements 

 by the influence of their own ganglia. Or, again, if the head 

 of a Centipede be cut off, and, while it remains at rest, some 

 irritating vapour (such as that of ammonia or muriatic acid) 

 be caused to enter the air-tubes on one side of the trunk, the 

 body will be immediately bent in the opposite direction, so as 

 to withdraw itself as much as possible from the influence of 



