80 ADRENALIN IN ANNELIDS 



sympathetic nerve cells. He has therefore called the chromaffin 

 system the paraganghon system, in order to point out its intimate 

 relationship to the ganglia of the sympathetic chains. There is thus 

 a close parallel between the condition in Hirudo and the early embry- 

 ological development of these tissues in the mammal. The connec- 

 tions of the two types of cell with the central nervous system in the 

 vertebrate, which have already been referred to, also support the 

 theory that they have been derived from a common ancestral cell, for 

 both are supphed by medullated connector or tract fibers which run 

 out from the central nervous system to connect with them. 



During the investigation of the nervous systems of the various 

 members of the annelid groups, a vascular system with definite mus- 

 cular walls was found always to exist when chromaffin nerve cells 

 were present, but to be absent when such nerve cells were also absent. 

 The members of the Hirudineae investigated all possessed muscular 

 walled vessels, and Lumbricus has, as is well known, similar muscular 

 "hearts" which are rhythmically contractile. Eunice gigantia, one 

 of the two members of the polychsete group in which chromaffin nerve 

 cells were found, possesses a short portion of vessel at the base of each 

 of the branchijE, which is suspended on a mesentery and has definite 

 muscular walls. These vessels by their contraction drive blood into 

 the branchiae to be oxygenated. Contractile muscular walled vessels 

 are therefore present in this animal. The vascular system oi Aphrodite 

 could not be thoroughly investigated owing to lack of material; the 

 question of the presence of vessels with muscular walls could not 

 therefore be decided. In all the other members of the polychaete 

 group, which possessed any definite vessels at all, no sign of any 

 muscular tissue could be found on their walls. It appears that, 

 wherever vascular muscle is present in the Annelida, chromaffin nerve 

 cells are also to be found in the central nervous system, and that these 

 cells are adrenalin-secreting; on the other hand, if no vascular muscle 

 is present no chromaffin cells exist. These facts support the view 

 that the chromaffin nerve cells innervate the vascular muscles. 



Further investigations were made to attempt to discover the nature 

 of the innervation of the vascular muscles in the leech, and also their 

 reaction to adrenalin. The nervous system and vascular system were 

 investigated in detail and the results are described in full in my pre- 



