PHYSIOLOGY OF INSECTS. 137 



CHAPTER VII. 



OF NERVES, THE ORGANS OF SENSATION. 



511. IN vertebrated animals the brain is situated 

 in the head. Brain is supposed to be the seat of 

 mind : all the nerves originate in the brain : the 

 nerves are the organs of sensation. 



512. 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 the 

 whole length of the insect. 



513. Experience has shown us that, on the 

 brain of vertebrated 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 con- 

 taining either of these masses of nerves, produces 

 no immediate or ascertainable effect on sensation 

 or vitality. 



514. This shows us, first, that mind or volition 

 is, in vertebrated animals, situate in the brain ; 

 secondly, that in insects it is not confined to an 



