590 PROCEEDINGS OF THE AMERICAN ACADEMY. 



to the fixing fluid appeared to aid greatly in preserving the impregna- 

 tion. It was usually most convenient to use only the anterior portion 

 of the body in studying the velum, se^-ering the body a short distance 

 behind that structure. This anterior portion was prepared for study 

 under a dissecting microscope by cutting with fine scissors along the 

 longitudinal axis, usually on the right side, as close as possible to the 

 dorsal fin. Certain specimens were cut in different regions, so as to 

 make it possible to determine the com'se of the nerve branches on both 

 sides of the body. These preparations were arranged on a slide in 

 the preserving mixture, with the aid of camel's hair brushes. The 

 velar tentacles were arranged in the position showing the nerves to 

 best advantage. Thin supports beneath the cover-glass were usually 

 necessary to prevent injury. Strong light was found useful in follow- 

 ing the deep-lying nerve branches, but the velar plexus, Avhen im- 

 pregnated, is usually visible with ordinary light. The velar nerves 

 require a long immersion in the methylene-blue mixture (1^ to 2| 

 hours), with a subsequent exposure to air of about one hour. Unless 

 osmic acid is added to the fixing fluid, the epithelial co\ering of the 

 velum sloughs ofi^ to a large extent. 



Although considerable variation exists in the innervation of the 

 velum. Figure 8 (PI. 2) presents a fairly typical picture of the branches 

 of the dorsal ner^'es which pass to this structure, and the distribution 

 of the nerves in the velum itself. Figure 9 shows the nerxes of a large 

 and a small velar tentacle in greater detail. These figures present 

 the first published views of the entire plexus of the velar muscle, and 

 of the nerves of the velar tentacles. These figures do not show the 

 epithelial covering of the velum, except for occasional cells apparently 

 remaining attached to nerve branches. 



Figure 8 may be taken as a basis for the description. In this speci- 

 men branches of the ventral rami of left ner^■es ^' and ^T suppl\' the 

 velum. A somewhat complicated alternation of anastomosis and 

 division takes place between these branches as they pass to the velum. 

 A large branch of left nerve V takes a course along the ventral muscle 

 border to the ventral ramus of left nerve VI, and anastomoses with the 

 latter. Tw^o branches destined for the velum are gi^'en olf near this 

 place of union. The larger (a) takes a backward course along the ven- 

 tral border of the trunk muscles for a short distance, and then bends 

 around the muscle border to the inner surface of the side muscles, where 

 it is continued posteriorly with considerable deflection dorsalward. 

 As it bends toward the interior, this large l)ranch gives off a much 

 smaller one (7), which passes posteriad and ventrad, di\iding after 



