KUTCHIN. — PERIPHERAL NERVOUS SYSTEM OF AMPHIOXUS. Gil 



to If hours. The subsequent exposure to air varied from 15 to 40 

 minutes. The specimens were fixed in ammonium picrate to which a 

 httle osmic acid had been added, or in ammonium molybdate and 

 osmic acid. Direct sunhght, a Welsbach lamp, or a Nernst lamp were 

 used in studying whole specimens. 



The distal ends of the finer cutaneous nerve branchlets are often 

 noticeably directed toward the exterior (PI. 7, Fig. 37). By focusing 

 on the plane in which the exterior ends of these nerve branchlets lie, 

 it may be observed that the surface of the cuticula is broken by 

 numerous small clefts crossing each other either at right angles, or in 

 the form of an X. By focusing downward upon a dark spot at the 

 place of crossing, it can be determined that this spot is the end of a 

 nerve branchlet, which can be followed to its place of union with one 

 of the larger branches. These numerous small, exteriorly directed 

 branchlets for the most part, therefore, penetrate the sub-epithelial 

 so-called cuticula (better basement membrane) through the small 

 canals first described by Langerhans. These small branchlets are 

 more numerous than either Heymans et van der Stricht ('98), or 

 Dogiel ( : 02) have figured. They were not always evident, and it was 

 frequently impossible to demonstrate a basement membrane, which 

 seems to indicate that this structure sometimes sloughs off with the 

 epithelium. Figures 34 (PI. 6) and 39 (PI. 7), wliich show these 

 exteriorly directed small branchlets in considerable numbers, also 

 show other characteristic cutaneous nerve branches. I refer to large 

 branches, lying close to the muscles, which may be noted connecting 

 the branches of two or more dorsal nerves in their course over the side 

 muscles (see also PI. 6, Fig. 36, jh and PI. 7, Fig. 38, pi). Beside these 

 connecting branches, there are, lying at a higher focus, finer plexuses, 

 which connect the small, exteriorly directed branchlets. These finer 

 plexuses may also be seen in Figures 35, jjo and 38, ;>• In methylene- 

 blue preparations this finer plexus is usually the most superficial nervous 

 structure visible. The branches of the deeper plexus are usually of 

 considerable size, and fewer in number than those of the more exterior 

 plexus, and their meshes are larger than those of the outer plexus. 

 As has been noted, the deeper plexus lies close to the muscles, and its 

 branches may even run beneath other large branches of the dorsal 

 nerves. This plexus between the ventral rami of dorsal nerves was 

 found distributed over the side muscles in nearly all parts of the body. 

 The finer plexus is composed of slender threads, forming close meshes ; 

 it was found in the regions where there is a coarser plexus, and also 

 in the ventral fin, and l:»etween the dorsal rami of dorsal nerves. The 



