CHAPTER VI. 



THE NERVOUS SYSTEM OF ARTHROPODS. 



THE next sub-kingdom, ARTHROPODA, comprises the 

 Myriapods, Crustacea, Spiders, and Insects. They are all 

 characterized by the possession of hollow and jointed 

 organs of locomotion provided with distinct muscles, 

 instead of the mere lateral setae or bristles often met with 

 amongst Vermes. The lowest types of these various 

 classes possess a nervous system closely analogous to 

 that of the various kinds of Worms ; but in the higher 

 kinds of Crabs, Spiders, and Insects, we meet with a 

 great increase in the complexity of animal organization, 

 and this further complexity, as might have been expected, 

 extends to the nervous system. 



Among Insects, for example, the respiratory organs 

 assume a marvellous degree of elaboration, and the develop- 

 ment of this system, together with a correlated organiza- 

 tion of their nervous and muscular systems, contributes 

 greatly to confer upon these denizens of the air those enor- 

 mous powers of locomotion for which they are remarkable. 

 But the acuteness, discriminative power, and structural 

 elaboration of sense-organs, is almost sure to be greatly 

 increased in creatures endowed with such activity ; and, 

 looking to the constitution of the Brain as well as to 

 the nature of the ' intelligence ' of these lower animals, it 

 may easily be conceived that increased sensorial activity is 



