270 REPORT — 1851. 



abdominal ganglia. These last act unquestionably on a purely physical 

 principle. Their agency is exclusively excito-motory. Each ganglion is 

 limited in its influence to the annulus to which it belongs. The stimulus 

 of external contact aflecting the extremities of its afferent fibres determines 

 the return force, the reaction, conveyed to the muscles through the medium 

 of the efferent nerves. Though thus automatic in the principle of their 

 action, the cephalic masses nevertheless exercise over the abdominal ganglia 

 an interfering influence. The force of the former mingles with that of the 

 latter with a view to its guidance and direction ; muscular agency is thus 

 moderated and governed. The automatic force originating in the abdominal 

 ganglia confers on the muscles the power of contraction ; the sensational or 

 instinctive influence of the cephalic masses directs this blind power, such as 

 that consensual harmony and coordination may result from the intricate 

 evolutions. 



The laborious researches of Mr. Newport on the Nervous System of the 

 Myriapoda* apply with equal exactness to that of the Annelida. Expound- 

 ing the views of Mr. Newport and announcing his results, Dr. Carpenter 

 observes-}-, " The general conformation of the articulated animals and the 

 arrangements of the parts of their nervous system render them peculiarly 

 favourable subjects for the study of the reflex actions, some of the principal 

 phsenomena of which will now be described. The Mantis religiosa customa- 

 rily places itself in a curious position, especially when threatened or attacked, 

 resting upon its two posterior pair of legs and elevating its thorax with the 

 anterior pair, which are armed with powerful claws. Now if the anterior 

 segment of the thorax with its attached members be removed, the posterior 

 part of the body will still remain balanced upon the four legs which belong 

 to it, resisting any attempt to overthrow it, recovering its position when dis- 

 turbed, and performing the same agitated movements of the wings and elytra 

 as when the unmutilated insect is irritated ; on the other hand, the detached 

 portion of the thorax, which contains a ganglion, will, when separated from 

 the head, set in motion its long arms and impress their hooks on the fingers 

 which hold it. If the head of a Centipede be cut off whilst it is in motion, 

 the body M'ill continue to move onward by the action of the legs ; and the 

 same will take place in the separate parts if the body be divided into several 

 distinct portions. After these actions have come to an end they may "be 

 exerted again by irritating any part of the nervous centres or the cut ex- 

 tremities of the nervous cord. The body is moved forwards by the regular 

 and successive actions 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 forward movement is checked by an interposed obstacle. Hence, 

 although they might seem to indicate consciousness and a guiding will, they 

 do not so in reality, for they ai-e carried on as it were mechanically, and show 

 no direction of object, no avoidance of danger. If the body be opposed in 

 its progress by an obstacle of not more than half of its own height, it mounts 

 over it and moves directly onwards as in its natural state ; but if the obstacle 

 be equal to its own height, its progress is arrested, and cut extremities of the 

 body remain forced up against the opposing substance, the legs still con- 

 tinuing to move. If, again, the nervous cord of a Centipede be divided in the 

 middle of the ti-unk, so that the hinder legs are cut oft' from connexion with 

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

 those of the fore-part of the body, being completely paralysed, so far as the 

 animal's controlling power is concerned, though still capable of performing 

 * See Newport in the Philosophical Transactions for 1843. 

 t Principles of General and Comparative Physiology. 



