EXPERIMENTS ON WORMS 



^K^L.-^. o. 



ganglia and from these to those farther away, until at 

 last it reaches the end of the animal. 



The central nervous sys- 

 tem of Annelids corre- 

 sponds to the spinal cord 

 of Vertebrates and consists 

 simply of a chain of ganglia. 

 These lie entirely on the 

 ventral side of the animal, 

 with the exception of the 

 most anterior (supraceso- 

 phageal) ganglion (Fig. 

 26), which lies above the 

 oesophagus on the dorsal 

 side. This is connected 

 with the subcesophageal 

 ganglion by a double com- 

 missure, which forms a loop 

 through which the oesopha- 

 gus passes. It may be 

 called the brain, although 

 the small analogy exist- 

 ing between Vertebrates 

 and worms makes the use FlG 26 THE BRAIN AND A SERIES 



of the term purely arbi- OF SEGMENTAL GANGLIA OF AN 

 j- rqrv ANNELID (NEREIS). 



A. r r i 0, supraoesophageal ganglion or brain ; c, 



question of funda- c l missure 7 , BuboeLphageai g a ng iion. 



mental interest to us arises ( After cla P artde -> 

 at this point : Is the brain simply a segmental gan- 

 glion, or is it an organ of a higher order which 



