596 PROCEEDINGS OF THE AMERICAN ACADEMY. 



This branch runs for some distance inside a gonadial pouch. The 

 descencUng branch passes downward over the inner surface of the most 

 ventral myomere to the inner surface of the transverse muscles. Here 

 it appears to lie between layers of connective tissue. Both the as- 

 cending and descending visceral rami show a faint bluish tinge in 

 sections stained with Mallory's differential stain, due, perhaps, to the 

 presence of a thin connective-tissue sheath. 



The distribution of the branches of the rami viscerales desccndentes, 

 forming the inner abdominal plexus, has been well described by 

 Fusari ('89), Heymans et van der Stricht ('98), and Dogiel (:02). 

 Fusari and Dogiel note a network of extremely fine threads connected 

 with the coarser meshes of the inner abdominal plexus. Dogiel 

 describes these threads as somewhat varicose. He also finds other 

 fine branchlets given off from the coarser plexus, which run to the 

 abdominal muscles, and break up into a great number of repeatedly 

 dividing finer tlireadlets that possess small varicose thickenings. 

 Dogiel is of the opinion that these threadlets weave about the trans- 

 verse muscles in an exceptionally thick plexus, analogous to that 

 which he has described for the "ring-muscle" of the mouth. He 

 does not find the fibers described by Heymens et van der Stricht as 

 passing directly from the coarser plexus to penetrate between the 

 lamellae of the transverse muscle, where they terminate in swellings 

 analogous to the endings of nerve fibers in smooth muscle. Dogiel 

 notes small three-cornered nuclei in the angles formed by branchlets of 

 the coarser abdominal plexus. Fusari finds no ganglion cells in con- 

 nection with this plexus, but notes small nuclei at the knotted places 

 of anastomosis. He designates the nerves of the inner abdominal 

 plexus as sympathetic. 



The finer plexus described by Fusari and Dogiel is clearly visible in 

 certain of my methylene-blue preparations. In these preparations 

 the threads of this finer plexus are less varicose than those figured by 

 Dogiel (:02, Fig. 14, 15). However, at rather infrequent intervals 

 swellings resembling small nuclei may be seen. Many of these finer 

 threads cross the interior faces of the coarser meshes, indicating that 

 they lie closer to the epithelium covering the inner surface of the 

 transverse muscles than does the main plexus. A few fine threads, 

 however, cross the external surfaces of the larger meshes. The 

 meshes of the finer plexus are generally elongated parallel to the long 

 axis of the animal. A secondary plexus is also present in that portion 

 of the abdominal region which lies between the transverse muscles of 

 either side of the body, but its meshes do not appear to be as close 



