1 5 4 THE INVOL UNTAR Y NER VO US S YS TEM 



cerned, and not to any action of the nerve on the vascular muscle 

 itself. In the case of the heart, where the vascular muscle is the 

 organ itself, we see clear proof of the reciprocal innervation by 

 the two systems, for the motor cells belong to the sympathetic 

 system, and are situated in the lateral chain of ganglia, while the 

 inhibitory cells are situated in the heart itself and belong to the 

 vagus nerve and therefore to the enteral system. 



I pass now to the musculature of the enteral system the 

 endodermal muscles. Their motor cells have travelled out as far 

 as the muscles themselves, and in the case of the large intestine 

 have been accompanied by the inhibitory cells of the sympathetic 

 musculature, the pelvic plexus contains both the motor cells to 

 the endodermal muscle of the large intestine and bladder as well 

 as the inhibitory cells to the sphincter musculature of the same 

 organs. Here again we see the same suggestion of the travelling 

 out of a single nerve cell which gives origin to motor nerves to 

 endodermal musculature and inhibitory nerves to opposing mus- 

 culature. At present we cannot speak of the inhibitory nerve 

 cells of the ileo-colic sphincter, for they have not yet been 

 traced. 



In other cases of endodermal musculature we find indications 

 of reciprocal innervation between the enteral and sympathetic 

 systems ; thus the motor cells of the endodermal musculature, 

 whether in the lungs (bronchial muscles) or in the liver (muscles 

 of the gall bladder and duct), have travelled out right into the 

 muscles themselves and their inhibitory nerves come from the 

 nerve cells of the sympathetic system. The exception to the 

 rule is found in the behaviour of the endodermal musculature of 

 that portion of the alimentary canal which is anterior to the 

 stomach. Here apparently both inhibitory and motor fibres be- 

 long to the enteral system, and the sympathetic does not send 

 any fibres to it. 



The fact that certain nerve cells in the central nervous system 

 of segmented annelids contain adrenaline, and that the presence 

 of such nerve cells is correlated with the presence of muscular 

 tissue in the vascular systems, points most strongly to the con- 

 clusion that here in the annelid group we are watching the 

 genesis of the sympathetic nervous system. My whole theory of 

 the origin of vertebrates is based on an ancestor, which itself 

 had arisen from the segmented annelid group, and on this 



