6o BRISTOL. [Vol. XV. 



cells. The same characteristic difference between the fiber 

 bundles which run forward and the plexuses is found at each of 

 the other branches, and similar but smaller ganglionic masses 

 are present. Back of the collar, the muscular wall of the 

 alimentary canal is covered with a complicated meshwork, as 

 shown in PL VII, Fig. 17, and shown in greater detail in PL 

 VIII, Fig. 20. The cells are multipolar and send processes in 

 various directions, forming meshes. The processes ramify the 

 wall and innervate the muscle cells. The preparations made 

 with formic acid are not satisfactory for histological detail, and 

 Fig. 20 is introduced to show the distribution, not the structure. 



This system continues over the whole alimentary tract in 

 substantially the same manner as shown on the oesophagus, 

 and though from theoretical considerations I expected and 

 sought diligently for metameric connections from the central 

 system, I am confident that none exist. 



In a few very favorable sections I have seen what I believe 

 are traces of the sympathetic system in the post-anal region, 

 extending in the axial line of the acetabulum and the sucker. 

 The musculature in this region is so complicated that I cannot 

 determine this point to my complete satisfaction. Nerve cells 

 and fibers are certainly there and show plainly. There is no 

 theoretical objection to their being a part of the sympathetic, 

 for if in the ancestral form the anus was terminal and the 

 sympathetic system was present to the anus, then in the leech 

 the formation of the sucker undoubtedly made demands upon 

 the muscles of the alimentary tract that may have continued 

 after the anus moved forward and the sucker became imperforate. 

 Again, while feeding, the leeches always hold themselves fast 

 by the sucker, and the stronger stimuli to the muscles excited 

 by food in the alimentary tract, during a meal, may by this 

 same system be communicated to part of the muscles of the 

 sucker and may help to make the adhesion more effective. 



