610 PROCEEDINGS OF THE AMERICAN ACADEMY. 



branchlets, which He immediutely beneath the epithelium, in turn 

 divide repeatedly in this rejjion, giving oft" fine, varicose threads, 

 which form a close-meshed plexus. This is designated by Dogiel 

 as the "sub-epithelial plexus." From this plexus fine threadlets 

 penetrate lietween the epithelial cells, and there give off side branchlets, 

 which twist about these cells and end betAveen them; these threads 

 were followed almost to the outer surface of the skin. Dogiel found 

 such endings in the rostrum, in the middle region of the body, and in 

 the tail. But in addition to these free nerve endings in the epithelium, 

 Dogiel also saw in the epithelium what he regards as peripheral nerve 

 cells; these occur in the rostrum, the tentacles, and the "head" 

 region. He believes that they are scattered over the entire skin area. 

 These cells have a spindle-shaped body, with a peripheral and a central 

 process, and a large nucleus, nearly filling the thick part of the cell. 

 The peripheral process is a short, thick cylinder or rod, which reaches 

 close to the outer surface of the epithelium, and its end is either blunt, 

 or somewhat pointed, but it never extends in the form of a thread 

 beyond the free surface of the skin. The central process runs per- 

 pendicularly or obliquely toward the interior, and could occasionally 

 be seen passing through the homogeneous layer of the skin and uniting 

 with a nerve branchlet. Dogiel's Figur 28 presents a portion of the 

 "sub-epithelial plexus" and its branches in the ventral region of the 

 body, in connection with the well-known plexus formed from branches 

 of the rami cutanei A'cntrales. His figures 29 and 30 show peripheral 

 nerve cells in the skin of the rostrum and head. Dogiel also illustrates 

 nerve-endings in the tentacles of the mouth. 



In my own study of the sensory nerve terminations in Amphioxus 

 a great number of methods were employed, including methylene-blue 

 impregnation, the methods of Golgi, the Aarious gold-chloride methods, 

 picro-carmine staining, and sections of material fixed and stained in a 

 variety of w^ays. As has been noted, the extensive arborescent 

 appearance of the cutaneous branches of the dorsal nerves may be 

 readily observed in methylene-blue preparations studied with the aid 

 of strong light (PI. 6, Fig. 34; PI. 7, Figs. 37, 39). The arrangement 

 of the sensory endings must depend largely on the distribution of the 

 finer terminal nerve branches. The extreme readiness with which 

 Amphioxus reacts to tactile stimuli applied to any part of the body, 

 indicates a rich supply of cutaneous nerves. The sensory nerve 

 branches reaching to the epithelial layer of the skin are most readily 

 followed in methylene-blue preparations. The best impregnations 

 of these nerves were obtained by immersion of the specimens from 1| 



