98 COMPARATIVE PHYSIOLOGY OF THE BRAIN 



In Vertebrates the head contains special sense- 

 organs, mouth-organs, which are lacking in the other 

 segments. In judging of the relation of the brain- 

 ganglia to the other segmental ganglia of the body 

 this fact should not be overlooked. Not infrequently 

 physiologists have ascribed to a ganglion what in 



reality was due to the 

 higher differentiation of 

 the peripheral organs of 

 the segment. 



We desire now to 

 touch briefly upon the 

 behaviour of the muscles 

 after extirpation of the 

 ganglion, for the phe- 

 nomena will occupy our 

 attention repeatedly. 



In the case of loss or 

 a congenital lack of a 

 piece of the spinal cord, 

 the skeletal muscles belonging to the corresponding 

 segment atrophy. Nothing of the kind occurs in 

 leeches or earthworms from whose ventral chain 

 a piece has been removed. I believe that the dif- 

 ference is determined as follows : In worms direct 

 impulses flow from the neighbouring muscles to the 

 muscles that have been deprived of their ganglion, 

 while in Vertebrates, as soon as the spinal cord is 

 destroyed, the protoplasmic connection between the 

 skeletal muscles and the rest of the body is destroyed 



FIG. 30. 



HEAD OF NEREIS. 

 Quatrefages.) 



(After 



