FUNCTIONS OF THE CORD. 311 



the body, being completely paralyzed, so far as the animal's controlling 

 power is concerned, though still capable of performing reflex movements 

 by the influence of their own ganglia, which may thus continue to propel 

 the body in opposition to the determinations of the animal itself. The 

 case is still more remarkable when the nervous cord is not merely di- 

 vided, but a portion of it is entirely removed from the middle of the trunk ; 

 for the anterior legs still remain obedient to the animal's control, the legs 

 of the segments from which the nervous cord has been removed are alto- 

 gether motionless, while those of the posterior segments continue to act 

 through the reflex powers of their own ganglia, in a manner which shows 

 that the animal has no power of checking or directing them. 



" The stimulus to the reflex movements of the legs in the foregoing 

 cases appears to be given by the contact of the extremities with the solid 

 surface on which they rest. In other instances the appropriate impression 

 can only be made by the contact of liquid. Thus a dytiscus (a kind of 

 water-beetle), having had its cephalic ganglia removed, remained motion- 

 less as long as it rested upon a dry surface, but when cast into water it 

 executed the usual swimming motions with great energy and rapidity, 

 striking all its comrades to one side by its violence, and persisting in 

 these for more than half an hour. Other movements again may be ex- 

 cited through the respiratory surface. Thus, if the head of a centipede 

 be cut off, and, while it remains at rest, some irritating vapor (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 direc- 

 tion, so as to withdraw itself as much as possible from the influence of 

 the vapor ; if the same irritation be then applied to the other side, the re- 

 verse movement will take place, and the body may be caused to bend in 

 two or three different curves by bringing the irritating vapor into the 

 neighborhood of different parts of either side. This movement is evi- 

 dently a reflex one, and serves to withdraw the entrances of the air-tubes 

 from the source of irritation, in the same manner as the acts of coughing 

 and sneezing in the higher animals cause the expulsion from the air-pas- 

 sages of solid, liquid, or gaseous irritating matters which may have found 

 their way into them. 



"From these and similar facts, it appears that the ordinary movements 

 of the legs and wings of articulated animals are of a reflex nature, and 

 may be effected solely through the ganglia with which these organs are 

 severally connected ; while, in the perfect being, they are harmonized, 

 controlled, and directed by impulses which act through the cephalic gan- 

 glia, and the nerves proceeding from them. There is strong reaeon to 

 believe that the operations to which these ganglia are subservient are al- 

 most entirely of a consensual nature, being immediately prompted by 

 sensations, chiefly those of sight, and seldom or never by any processes 



