REFLEX 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completely withdrawn from any control on the part of the 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 
