600 PROCEEDINGS OF THE AMERICAN ACADEMY. 



plexus on their more interior surfaces appears continuous and the 

 origin of branches from the visceral rami is largely hidden. Figure 13 

 (PI. 3) shows only the larger meshes of the plexus on the internal 

 surface of a gonadic pouch, but the origin of these branches is illus- 

 trated. In Figure 10 (PI. 2) the finer meshes of this plexus are shown 

 under greater magnification. In methylene-blue preparations the 

 threads of the gonadic plexus often appear faintly granular, indicating 

 that they impregnate in a manner similar to the nerves of the inner 

 abdominal plexus. Heymans et van der Stricht ('98) find the "peri- 

 toneal" plexus less rich under the sexual glands, but in this they 

 probably refer only to the larger meshes. These authors do not 

 figure the origin of branches running to the gonadic pouches, and give 

 no detailed account of their innervation. Dogiel ( : 02) does not 

 discuss the innervation of these organs. 



The main stem of an ascending visceral ramus may usually be fol- 

 lowed dorsad a distance equal to the width of one, two or even three 

 myomeres from the ventral border of the side muscles, and then it 

 breaks up into a large number of branches spreading out fan fashion 

 over the inner surface of these muscles. In the anterior part of the 

 body these fans are directed somewhat anteriad as well as dorsad 

 (PI. 4, Fig. 15), but the branches of the more posterior ascending 

 visceral rami take in general a dorsad direction. If the wall of the 

 branchial basket is lifted to disclose these nerves, the numerous 

 branches of a fan often appear broken off abruptly in the middle 

 region of the side muscles, and the distal broken ends are most fre- 

 quently bent away from the muscles as though lying in a membrane 

 not closely attached to the side muscles. This is no doubt due to the 

 entrance of these nerves into the ligamentum denticulatum. As may 

 be noted in Figure 15, c and d, the branches of one fan anastomose 

 with those of an adjoining fan, thus forming a continuous network 

 along the inner surface of the side muscles, and in the ligamentum 

 denticulatum. This plexus may or may not lie dorsal to the gonadic 

 pouches, depending on the size of the pouches. As has been mentioned, 

 these fans join nerve threads which innervate the sexual glands. 



From the plexus formed by these fans, certain branches pass upward 

 along the ligamentum denticulatum (PI. 4, Figs. 16, 17), while others 

 ramify extensively in the "pocket" portions of this ligament. These 

 nerves often present a fibrous appearance, as noted by Fusari; but 

 this seems to depend on the time or manner of fixation. In other cases 

 they appear dotted, with rough edges, the latter perhaps due to the 

 deposit of a small quantity of coloring matter in the surrounding 



