OF THE NERVES. 181 



the nerves originate in the brain : the nerves are the organs 

 of sensation. We find that in insects there is no part 

 positively ascertained to be the brain : we discover nerves 

 throughout the body, and we trace these to large masses or 

 knots, situated at intervals throughout the whole length of 

 the insect. 



Experience has shown us that, on the brain of verte- 

 brated animals being separated from the body, or even 

 greatly injured, both sensation and active vitality at once 

 cease ; but in insects the separating of the head or of the 

 parts containing either of these masses of nerves, produces 

 no immediate or ascertainable effect on sensation or vi- 

 tality. This shows us, Jirst, that mind or volition is, in 

 vertebrated animals, situate in the brain ; secondly, that in 

 insects it is not exclusively confined to any part. These 

 conclusions lead to the probability of a third, that brain and 

 nerve are but difierent states of the same system of organs. 

 The vitality, therefore, concentrated in a brain, may be dif- 

 fused through the nerves when there is no brain, and each 

 mass of nerves may be the seat of that small power of 

 mind which insects possess. 



The neiTous cord extending, as described, from one end 

 of the insect to the other, is compared to, and has been 

 called, the spinal marrow ; its first knot or incrassated 

 portion, the brain; the following knots, ganglions: this 

 nomenclature appears arbitrary, as we have seen that no 

 particular portion exercises exclusively the functions of a 

 brain. It appears better to consider each of the little 

 knots a separate and independent centre of volition, as it 

 undoubtedly possesses the characters of such, giving out 

 its various nerves in the same manner as the human brain. 



All anatomical operations succeed best with the larvae of 

 insects, because the constant and obvious division of the 

 body of larvae into thirteen segments, affords us more ready 



