KUTCHIN. — PERIPHERAL NERVOUS SYSTEM OF AMPHIOXUS. G13 



The plexuses shown in Figures 34, 38, and 41 — formed by the break- 

 ing up, for a short distance, of the main stem of the ventral ramus of a 

 dorsal nerve into a number of anastomosing branches, — are of fre- 

 quent occurrence, but do not appear to have been noted by earlier 

 authors. Such plexuses may have a morphological significance, or 

 they may be pathological, the result of injury or disease. A simpler 

 form of division of the ventral ramus is often present, in which the 

 main stem divides into two branches of nearly equal size, which unite 

 again after a short course. These modifications in the ventral ramus 

 often serve to attract attention to fine plexuses in connection with 

 them. "Rami communicantes " were often noted in both species. 



In the figures showing plexuses between the dorsal nerves, brandies 

 may often be noted, in connection M'ith at least the coarser plexus, 

 which penetrate the myosepta toward the interior of the muscle 

 (a. Figs. 34, 36, PI. 6). The destination of these branches is uncertain. 



The absence, in methylene-blue preparations, of any great number 

 of branches arising from the finer plexuses, is of interest. It may, 

 perhaps, be accounted for by the fact that such thick preparations 

 are not fa-\'orable for disclosing fine threadlets; higher magnifications 

 of course cannot be used. Gold-chloride preparations of the skin were 

 made to supplement those on which are based the foregoing account 

 of terminal branches. The method of Ranvier was used, also that of 

 Hardesty, in which impregnation with gold chloride follows fixation 

 with 10% formol. The latter method gives accurate fixation as a 

 rule, and the finer cutaneous nerve branches often adhere to the skin, 

 when it is stripped off, instead of remaining attached to the muscles. 

 Such preparations can be studied with the aid of the higher magnifica- 

 tions; but the epithelial cells always obscure the nerves more than is 

 desirable. Figure 24 (PI. 5) is drawn from a gold-chloride preparation 

 of material fixed in formol. This figure shows the internal surface of 

 skin stripped from the dorsal fin toward the posterior end of the animal. 

 A few epithelial cells are outlined (at c) to show their relative size, 

 and special cells, to be described later, are indicated at g (upper part 

 of figure). The fine threads apparently running out from the larger 

 nerve branch are the most delicate threads so far noted in connection 

 with the cutaneous l)ranches of dorsal nerves; and the star-like places 

 of anstomosis (s) of these threads remind one of those described by 

 Dogiel. Apparent cells or nuclei (c) may be noted in connection with 

 these threads, as the latter run to the special cells (indicated at g) 

 situated between the epithelial cells of the skin. Unfortunately, 

 however, connective-tissue threads stain very well with gold chloride, 



