130 Chapter VII. 



physiological transformation, and thereby convey the 

 colors of the object and, in some degree, its form and 

 figure to the perception of the subject whose sight or- 

 gan receives them. 



What has been said of the outer organs of sense 

 perception is equally applicable to the nervous system 

 of ants. Let us compare it with that of the higher 

 mammals and of man. The central nerve system of all 

 vertebrates is a cerebro-spinal, and that of all articu- 

 lates a cerebro -ventral medulla. Or, in other words, the 

 position of the medullary cord is dorsal, along the back, 

 in vertebrates, whilst it is ventral, along the front, in 

 articulates. The brain of insects is an oesophageal 

 nerve-centre, and consists of two double ganglia, one 

 above and one below the oesophagus. The upper 

 double ganglion is more developed and takes the place 

 of the cerebrum (anterior brain) of vertebrates. This 

 analogy between the cerebrum and the supra-oesoph- 

 ageal ganglion of insects is the more perfect, the 

 stronger the latter is developed. It displays its highest 

 perfection in the "workers" of social insects, and in 

 other art-loving Hymenoptera, whose supra-oesophageal 

 ganglion is not only relatively large, but marked, more- 

 over, by peculiarly developed parts called "peduncles" 

 (corpora peduncula). Still the point at issue in 

 comparative animal psychology is not so much the 

 anatomical difference of the nervous system of insects 

 and vertebrates, as rather its centralization and the rel- 

 ative size of the brain and the supra-oesophageal gang- 

 lion, in comparison to the other secondary ganglia. The 

 unity of sensitive consciousness in animals is in direct 

 proportion to the centralization of the nervous system ; 



