COMPARATIVE ANATOMY AND PHYSIOLOGY. Ill 



tic movements of these parts, which are performed in direct respondence to 

 external impressions, are only dependent for their stimulation upon that gan- 

 glionic centre with which the nerves that excite them are immediately con- 

 nected. Another instance, related by Burmeister, is still more satisfactory in 

 regard to the manner in which these movements are excited. A specimen of 

 the Dytiscus sulcatus, from which the cephalic ganglia had been removed, 

 and which remained in a motionless condition whilst lying with its abdomen 

 on a dry hard surface, executed the usual swimming motions, when cast into 

 water, with great energy and rapidity, striking all its comrades to one side by 

 its violence, and persisting in this for half an hour. 



146. These conclusions are also fully confirmed by the experiments of Mr. 

 Newport, upon various Insects and Myriapoda ; the results of which have 

 been recently made public.* The following, upon the Julus terrestris, is 

 particularly interesting. " The cord was divided in the fourteenth and also 

 the twentieth segment ; and the intervening portion was destroyed by break- 

 ing it down with a needle. The animal exhibited, in the anterior part of its 

 body, all the evidences of perfect volition. It moved actively along, turning 

 itself back on either side repeatedly, as if to examine the anterior wounded 

 portion, which it felt again and again with its antennae ; and when attempting 

 to escape, frequently turned back as if in pain and aware of some hindrance 

 to its movements ; but it seemed perfectly unconscious of the existence of the 

 posterior part of its body, behind the first incision. In those segments in 

 which the cord was destroyed, the legs were motionless ; while those of the 

 posterior division, behind the second incision, were in constant but involuntary 

 motion, the movements being similar to those of walking or running, uniformly 

 continued, but without any consentaneous action with those of the anterior 

 part, by which locomotion was performed, dragging the posterior divisions of 

 the body after them. When the animal was held by the posterior segments, 

 reflex actions were excited in the legs, and powerful contractions and gyra- 

 tions of the whole animal were performed in those segments ; but these move- 

 ments appeared to be entirely the result of reflex actions of the muscles, since 

 exactly similar ones took place in the whole body of decapitated specimens. 

 At the expiration of twelve hours, the most perfectly voluntary acts were per- 

 formed by the head and anterior division of the body, such as locomotion for- 

 wards or to either side, avoidance of any obstacle, touching it with the anten- 

 nas, (which were in rapid action, as in an uninjured animal,) and attempting 

 to reach and to climb up an object presented to it, but not in immediate con- 

 tact with it. But reflex movements alone existed in the posterior division, in 

 which the legs were very slowly moved, even when the animal was not pro- 

 gressing. Brisk actions were now more easily excited in them than at first, 

 either by contact with the segments, by irritation of one or two of the legs 

 themselves, or by a sudden current of air. By these means, when the animal 

 was lying still, actions were immediately excited in all the legs of the poste- 

 rior parts of the body, anterior and posterior to those which were irritated ; and 

 these actions were induced in those of both sides of the body, but appeared to 

 commence on the opposite side, in the legs corresponding to those which were 

 first irritated. In eighteen hours, the anterior part of the body was quite 

 dead, so that no motions whatever could be excited in it, either voluntary or 

 reflex ; but reflex actions were then readily excited in the posterior, and also 

 slightly so by mechanical irritation, even at twenty-four hours." It would 

 appear, then, that we may obtain more decided proof, in the Articulated series, 

 of the real character of reflex actions, and of their dependence upon a distinct 

 system of nerves, than we can draw from any other class of animals. In the 

 Vertebrata, it is easy to distinguish the sensory from the motor, the afferent 



* Philos. Trans., 1843, p. 267. 



