35 



two of these nerves were contained in one sheath, although fulfilHng 

 entirely different functions ; one at the posterior ministering to the 

 purposes of sensation, and the other, at the anterior, ministering in 

 response to tho contraction of the corresponding muscles. 



Next, they approached that important doctrine which was called 

 the " excito-motor "— the sensory nerve conveying the impression from 

 without to the ganglionic matter, which impression was responded to 

 by a mysterious action in the motor, or those nerves the filaments of 

 which supplied the muscular system that holds throughout. If they 

 examined the ventral cord of the higher insects,— so called from being 

 found in the ventral region,— two cords could be distinctly traced ; 

 and these were knotted into ganglionic little cells. Going on to the 

 thorax of insects, to which v,-ere fixed the legs and wings, they all knew 

 the remarkable activity of those limbs,— they found the ganglia aggre- 

 gating together to provide due energy for them. Advancing- to the 

 cephahc ganglion, there was a still further enlargement and evolution 

 of this nervous matter, it being the neighbourhood of that wonderful 

 organ, the insect's eye. It was under the guidance of visual impres- 

 sions that almost all the movements of insects were performed and 

 controlled, and thus they would observe how the proportion was kept 

 up between the ganglionic centre and the organ it supplied. 



With regard to this double cord in the insects, it was remarkable 

 that, in the embryonic stage of the human form, the spinal cord had 

 also two distinct lines, so that, in the former, they had an element of 

 what was the commencement of the human spinal cord ; while the 

 sensorium of the human brain corresponded with the cephalic ganglion 

 of the insect. In insects, the reflex action was automatic, all the 

 operations going on by virtue of the creature's structure, without the 

 interposition of an intelligent principle, the majority of the actions of 

 the social insects being thus explained. 



It was the same in the human brain ; but here they had the 

 superadded organ, the cerebrum, the material instrument of thought 

 and will ; and the degree of intelligence and self control corresponded 

 to the degree of development of that organ. It consisted of the 

 medullary matter, which was invested on its outer surface with a layer 

 of ganglionic cells, called cineritious, the medullary matter itself being 

 composed merely of nerve fibres, connected with the cortical substance 

 and the sensorium. From the sensorium radiated fibres going to the 



