2l6 MIRIAM F. NUZUM AND HERBERT W. RAND. 



esophageal commissures (c.c.) merge into the sub-esophageal gan- 

 glion (s.g.). (The section drawn is slightly anterior to the point 

 of union of the commissures.) The pharynx wall consists of an 

 epithelium (/>..) surrounded by a thin layer of muscle and con- 

 nective tissue (./>.). The epithelium itself (Fig. 2) is composed 

 of columnar cells with oval nuclei, most of which contain a promi- 

 nent nucleolus. They are, indeed, very similar to the cells of the 

 epidermis, perhaps being a trifle smaller. A point to be particu- 

 larly emphasized is that the nervous tissue of the brain is bounded 

 on the side toward the pharynx by enveloping layers of non- 

 nervous tissue, that the pharynx epithelium is bounded on the side 

 toward the brain by layers of non-nervous tissue, and between the 

 two organs is some free space. Nowhere is nerve tissue in inti- 

 mate association with the pharynx except where the lateral nerves 

 join it. 



Within a few hours after the operation the wound closes over, 

 and only a scar marks the region in which it was made. Cross- 

 sections of an early stage of regeneration, one week after the 

 operation (Fig. 3), show the epidermis entirely healed, but the 

 region of the wound (zy.) is readily distinguishable through the 

 absence of the characteristic gland cells. Below the epidermis, 

 extending down through the cut muscle layers, across the ccelomic 

 space and joining the pharynx wall, is a dense mass of deeply 

 stained cells (r.t.}. Fibers extending from the cut end of one 

 commissure pass through this cell mass just above the pharynx to 

 the cut end of the other commissure. There is little doubt that 

 these are nerve fibers and that they are outgrowths of cells of the 

 old nerve tissue. Lying approximately mid-dorsally and exactly 

 in the pathway of these fibers is a small and not definitely limited 

 group of cells (br.f.} made conspicuous by their especially in- 

 tensive staining. These cells, containing large nuclei with promi- 

 nent nucleoli, are similar to the cells of both pharyngeal and epi- 

 dermal epithelia. Their position, corresponding precisely to that 

 occupied by the obvious brain fundament of later stages, as well as 

 their character, marks them as the early brain fundament. (The 

 sections in this series were not exactly transverse. The section 

 represented in Fig. 3 contains a slightly lateral portion of the brain 

 fundament.) There is no line of demarcation between the brain 



