THE ORGANS OF SENSATION. 271 



ray observations in the caterpillar of Noctua Verbasci * . But they 

 can be clearly distinguished only in recently opened insects: in those 

 which have been long immersed in spirits of wine, the former darkens 

 by degrees, and the latter becomes discoloured, so that neither exhibit 

 any longer a difference. The cortical substance appears to be deficient 

 in the filaments, and merely the white milk-coloured core appears to be 

 present : these, therefore, are in general brighter, and do not at all 

 participate in the colouring of the ganglia. 



With respect to the general form of the nervous system of insects, it 

 presents itself as a double cord running along the ventral side, which 

 from segment to segment is re-united by ganglia. Two of these ganglia 

 lie in the head, one above the pharynx, the other beneath it, and together 

 form the brain, whence pass the nerves of the senses to the eyes, 

 antennae and oral organs. In the same way there spring from each of 

 the successive ganglia a number of lateral branches, which are subjected 

 to manifold differences, the three first of which pass to the legs, wings, 

 and muscles of the thorax ; those of the following ganglia to the 

 muscles of the abdomen, to the posterior end of the intestinal canal, 

 and to the organs of generation. The anterior portion of the canal, 

 namely, the crop and the stomach, has its peculiar nervous system, 

 which is formed by several auxiliary ganglia lying in the head. 



Our investigation of the nervous system will thence fall into the 

 following subdivisions. 



1. The brain with the nerves of the senses originating from it. 



2. The ganglionic ventral cord with its branches. 



3. The nervous system of the resophagus and stomach. 



To this we may add the organs of the senses themselves, of which 

 the eye alone will require a particular description ; as for the majority 

 of the remaining senses, no determinate organs have yet been fully 

 ascertained. 



1 This reminds us of the red nervous points in many of the lower animals, namely, the 

 Infusoria, especially the Rotatoria. Ehrenherg, in his admirable work upon these begin- 

 nings of organisation, considers these red points as eyes, but they are evidently nothing but 

 a mass of the nervous substance. 



