258 FUNCTIONS OF THE NERVOUS SYSTEM. 



trunks with the cephalic ganglia, as in the Mollusca ; and this must, there- 

 fore, conduct to the sensorium (whose seat is probably in the latter) the im- 

 pressions which there produce sensations, and must convey downwards the 

 locomotive impulse; whilst the ganglion of each segment, with the filaments 

 connected with its nucleus, will form the circle necessary for the simply- 

 reflex actions of its members. The independence of the segments of the 

 Articulata, as far as their reflex actions are concerned, and their common sub- 

 ordination to one presiding centre of the will, are fully explained on this sup- 

 position. It is also quite conformable to the analogy, both of Mollusca, and 

 of Vertebrata. 



328. The number and variety of the reflex actions, which take place in the 

 Articulata after decapitation, are very remarkable ; and they seem to have a 

 consentaneousness, proportioned to the closeness of the relation between the 

 nervous centres in the respective species. Thus, in the Centipede, w,e find 

 the ganglia of the several segments distinct, but connected by a commissural 

 trunk. Here an impression made equally upon the afferent nerves of all the 

 ganglia, will produce a consentaneous action. Thus, if the respiratory ori- 

 fices on one side of a decapitated Centipede be exposed to an irritating vapour, 

 the body will be immediately flexed in the opposite direction ; and if the 

 stigmata of the other side be then similarly irritated, a contrary movement 

 will occur. But different actions may be excited in different parts of the 

 cord, by the proper disposition of the irritating cause. In the higher classes, 

 however, where the ganglia of the locomotive organs are much concentrated, 

 the same irritation will produce consentaneous motions in several members, 

 similar to those which the unmutilated animal performs. In the Mantis 

 religiosa, for example, which ordinarily places ilself in a very curious 

 position, especially when threatened or attacked, resting upon its two pos- 

 terior pairs of legs, and elevating its thorax with the anterior pair, which are 

 armed with powerful claws, 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 attempts to over- 

 throw it, recovering its position when disturbed, and performing the same 

 agitated movements of the wings and elytra, as when the unmutilated animal 

 is irritated: on the other hand, the detached portion of the thorax, which con- 

 tains a ganglion, will, when separated from the head, set in motion its long 

 arms, and impress their hooks on the fingers which hold it. These facts 

 prove unequivocally, that the combined automatic movements of these parts, 

 which are performed in direct respondence to external expressions, are only 

 dependent lor their stimulation upon that ganglionic centre, with which the 

 nerves that excite them are immediately connected. Another instance, related 

 by Burmeister, is still more satisfactory in regard to the manner in which 

 these movements are excited. A specimen of the Dytiscits 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. 



329. 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 lulus terrestris, 

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

 also the twentieth segment; and the intervening portion was destroyed, by 

 breaking it down witli a needle. The animal exhibited in the anterior part. 



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



