PLATYHELMINTHES 



199 



remains permanently quiescent after the operation. This state of quies- 

 cence is not however due to a loss of co-ordination in the motor 

 system. Stimulation of the anterior end can evoke all the normal 



ce.ga.-/-- 



M.-l--, 



?— 



Fig. 145. The nervous system of Acoela, to show the nerve strands of the 

 network. After Steinmann. ce.ga. cerebral ganglion (brain); M. mouth; 

 (S and ?, male and female openings respectively. 



forms of locomotion, and this shows that the nerve net and not the 

 cerebral ganglion is responsible for the correlation of the different 

 parts of the musculature. The primitive central nervous system which 



