REFLEX ACTIONS OF ARTICULATA. 359 



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. Again, a specimen of Dytiscus (a water- 

 beetle), from which the cephalic ganglia have been removed, 

 executes the usual swimming motions when cast into water, 

 with great energy and rapidity, striking all its comrades to 

 one side by its violence ; in these it will persist for half an 

 hour, though so long as it lies on a dry surface it remains 

 quiescent. 



445. From these and similar facts, it appears that the ordi- 

 nary movements of the legs and wings of Articulated animals 

 are of a reflex nature, and are dependent upon the ganglia 

 with which these organs are severally connected ; whilst 

 in the perfect animal they are harmonised, controlled, and 

 directed by its conscious power, which acts through the 

 cephalic ganglia and the trunks proceeding from it. When 

 we come to compare the reflex movements of Insects with 

 those of the higher animals, we shall perceive that there is no 

 ground for supposing the ganglia of the trunk to be in them- 

 selves endowed with sensibility ; so that, when the head is cut 

 off, or the cephalic ganglia are removed, or their connexion 

 with any part of the body is interrupted by division of their 

 nervous cord, no sensation is felt, however much the move- 

 ments it performs may seem at first to indicate this. (See 

 467.) 



446. From this account of the structure and uses of the 

 chain of ganglia in the Articulata, it is obvious that these 

 ganglia are so many repetitions of the pedal ganglia (or gang- 

 lion of the foot) of the Mollusca ; and we have not yet had 

 to notice any ganglia appropriated to other functions. In fig. 

 186, however, is seen a small ganglion in front of the cephalic 

 mass, which corresponds to the pharyngeal ganglion of the 

 Aplysia (fig. 183, D) ; and we have now to describe an entirely 

 distinct system of nerves, appropriated to the function of respi- 

 ration. As the respiratory apparatus of Articulata, instead of 

 being confined to one spot, like that of the Mollusca, is dis- 

 persed througk the body ( 315 and 320), the ganglia which 

 minister to its actions are repeated in the several segments. 

 There is, in fact, a chain of minute ganglia lying upon the 

 larger cord, and sending off its nerves between those proceed- 

 ing from the latter, as seen in fig. 185. These respiratory 



