EXPERIMENTS ON WORMS 97 



of i:he supracesophageal ganglion and the repose after 

 the removal of the subcesophageal ganglion, we wish 

 to emphasise the fact that they have nothing to do 

 with the wound. Maxwell's observations were made 

 on animals whose wounds were healed. If we make 

 a wound like that made in removing the ganglion, 

 only with the difference that the ganglion is left intact, 

 none of the above-mentioned disturbances occur. 

 Immediately after the operation the worm burrows 

 again in spite of the wound. 



Differences like those found between the behaviour 

 of normal Nereis and of Nereis from which the brain 

 has been removed do not appear in earthworms under 

 the same conditions. What causes this difference ? 

 Is the supracesophageal ganglion in the earthworm 

 a segmental ganglion, while in Nereis it is a " control- 

 ling ganglion," a brain in the sense of the anthropo- 

 morphic nerve-physiology ? 



I am inclined to believe that we have to deal with 

 differences of the same character as those found 

 between Acalephae and Hydromedusae. In addition 

 it should be said that there is a much higher degree 

 of differentiation of the head-organs in Nereis than in 

 the earthworm. We have already seen in preceding 

 chapters that the apparent functions of the brain or of 

 the ganglia are chiefly determined by the peripheral 

 organs. In Nereis the differentiation of the head- 

 segments is carried much farther than that of the 

 other segments (Fig. 30). In the earthworm, on the 

 other hand, the difference is much less (Fig. 27). 



