102 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



supracesophageal ganglion also helps to increase 

 the predominance of the head-segments. Hence it 

 is not the presence of the supracesophageal ganglion 

 which determines the greater number of reactions 

 and their more complicated nature in the oral seg- 

 ments of some Annelids, but it is the presence of the 

 greater number of irritabilities and the greater number 

 of specific organs in the forward end of the body. In 

 addition there may exist chemical differences between 

 the various segments of an animal. 



We shall now see that this conception of the 

 central nervous system also holds good for the Ar- 

 thropods. We will begin the analysis of the brain- 

 functions of these forms with Limulus polypJicmus 



(Fig- 30- 



Zoologists maintain that Limulus is a very old form. 



If tenacity of life favours the age of the species as it 

 does the age of individuals, this assertion can be readily 

 understood, for it is difficult to conceive of a tougher 

 animal. At my suggestion, Miss Ida Hyde made ex- 

 periments on the functions of the single parts of the 

 central nervous system of Limuhis polyphemus, with 

 special attention to the respiratory centres (i). Con- 

 cerning these centres, Faivre had made assertions 



o 



which did not harmonise with the apparent segmental 

 arrangement of the central nervous system. He as- 

 sumes that the subcesophageal ganglion which is 

 located in the head has a coordinating influence 

 on the respiratory movements, but in forms like these 

 with the respiratory organs (gills) in the abdomen, 



