ii 4 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



and latterly Bethe (5) energetically reject the idea 

 that dorso-ventrally the ganglion-chain of Arthropods 

 is the reverse of the spinal cord of Vertebrates. 



4. We will now turn our attention to the crayfish 

 as the next representative of the Arthropods whose 

 brain-physiology has been carefully investigated. Fig. 

 32 gives a diagram of the central nervous system of 

 the lobster, which is almost identical with that of the 

 crayfish, o is the supraoesophageal ganglion with 

 the nerves for the eyes and antennae. In addition it 

 gives off the sympathetic nervous system which goes to 

 the intestine. Both cesophageal commissures, c, go 

 backwards to the subcesophageal ganglion, u. The 

 latter is seemingly one ganglion, but it supplies six 

 pairs of segmental organs, namely, the mouth-ap- 

 pendages. The microscopical examination shows that 

 this subcesophageal ganglion in reality consists of six 

 separate ganglia. We often meet with a fusion of 

 ganglia, and consequently an apparent lack of clear- 

 ness in the segmental arrangement. It is due to this 

 fact that in the brain-physiology of Vertebrates the 

 segmental arrangement of the central nervous system 

 has been left entirely out of consideration. Next 

 after the subcesophageal ganglion come the five 

 thoracic ganglia (I-V 7", Fig. 32) belonging to the 

 segments of the forceps and the four pairs of loco- 

 motor appendages. In addition to these, there are 

 the five ganglia of the abdomen (I-V Abd., Fig. 32) 

 that innervate the swimmerets, and the tail, which 

 serves as a swimming-organ. The best experiments 



