THE KILL! FISH 31 



the initial cutting or shortly thereafter, a second cut 

 in preparations of the kind described will be followed 

 by short dark streaks that can be traced into the region 

 of denervation (Fig. 25). As can be seen in fishes pre- 

 pared for this purpose and experimentally tested from 

 day to day, these dark bands extend farther and farther 

 each day till eventually they reach the edge of the fin 

 (Fig. 26). They are of 

 course due to the pres- 

 ence of melanophores 



" : v 



- 



with dispersed pigment 

 and reflect the progres- 

 sive regeneration of the 

 dispersing nerve-fibers. 

 Tn Fundulus, under the 

 circumstances described, 

 this regeneration begins 

 about the eighteenth day 

 after the initial cut and 

 is completed on about 

 the twenty-fifth day. 

 The approximate dis- 

 tance covered by the 

 growing nerve in these 

 seven days is some six 

 millimeters, and the rate 

 of regenerative growth consequently is about 0.8 milli- 

 meter per day (Parker and Porter, 1933). 



By an ingenious method that is an improvement over 

 the one just described, Abramowitz (1935) has made a 

 second determination of the rate of regeneration not 

 only for the dispersing fibers but also for the concen- 

 trating ones in Fundulus, for there is evidence, as we 

 shall see later, for two kinds of chromatophoral nerve- 

 fibers in this fish. In the method employed by Abramo- 



Fig. 26. Tail of a killifish 

 twenty-five days after a primary 

 cut had been made. The prox- 

 imal secondary cut induced the 

 formation of a complete new- 

 caudal band showing that the 

 regeneration of the dispersing 

 nerve-fibers had been fully estab- 

 lished. Parker and Porter, Jour. 

 Exp. Zool., 1933, 66, pi. 1, fig. 6. 



