THE NERVOUS SYSTEM 307 



mass present all degrees of perfection in the faculties derived from 

 them. 



I have already said that in its greatest simplicity the nervous system 

 appears to have its main medullary mass divided into several separate 

 parts, each of which contains an individual nucleus for the nerves 

 running into it. In this condition the system is not adapted for pro- 

 ducing sensations, though it has the faculty of setting the muscles 

 in action : now, does this very imperfect nervous system, which is 

 alleged to have been identified in the radiarians, also exist in the 

 worms ? I do not know ; and yet there are grounds for the belief, 

 unless the worms are a branch of the animal scale started afresh by 

 spontaneous generation. All I know is that in animals of the class 

 which follow the worms, the nervous system has reached a much 

 higher stage of development, and is quite easy to see and possesses a 

 very definite form. 



Indeed, as we follow the animal scale from the most imperfect to 

 the most perfect animals, the first appearance of the nervous system 

 has hitherto seemed to be in the insects ; because in all the animals of 

 this class it is very clearly defined, and presents a gangUonic longitudinal 

 cord, which as a rule extends throughout the animal's length and is 

 greatly diversified in shape according to the species of insect and to the 

 state of larva or perfect insect. This longitudinal cord, which ends 

 anteriorly in a subbilobate ganglion, constitutes the main medullary 

 mass of the system, and from its ganglia, which vary in size and 

 proximity, nervous threads proceed to the various parts of the 

 body. 



The subbilobate gangUon at the anterior extremity of the ganghonic 

 longitudinal cord of insects has to be distinguished from the other 

 ganglia of the cord, since it gives rise directly to a special sense — that 

 of sight. This terminal ganglion is, then, really a small and very 

 imperfect brain, and doubtless contains the centre of communication 

 of the sensitive nerves, since the optic nerve runs into it. Perhaps the 

 other ganglia of the longitudinal cord are in the same way special 

 nuclei, which provide for the action of the animal's muscles : if these 

 nuclei exist, they would not prevent the general effect which alone, 

 as I have proved, can produce feeling, since they are united by the 

 nervous cord. 



Thus in the insects, the nervous system begins to present a brain 

 and single centre of communication for the production of feeUng. 

 These animals, by the complexity of their nervous system, possess then 

 two distinct faculties, viz. : that of muscular movement and that of 

 experiencing sensations. These sensations are probably still only 

 simple and fugitive perceptions of the objects which aifect them, 



