32 COLOR CHANGES IN ANIMALS 



witz a Funduhis with a blanched caudal band, on which 

 the rate of regeneration in the dispersing nerve-fibers is 

 to be measured, is kept in a white-walled vessel. When 

 a measurement is to be made the fish is placed for five 

 minutes or more in a black-walled receptacle. Here it 

 naturally darkens, including such part of its caudal band 

 as has regenerated its dispersing fibers. The extent of 

 this part is measured and the fish returned to the white- 

 walled vessel where it remains till another measurement 

 is desired. The same method can be applied to the 

 concentrating nerve-fibers except that in this instance 

 the experimental fish is retained in a black-walled recep- 

 tacle and transferred temporarily for testing to a white- 

 walled one. In this instance the extent of the pale band 

 beyond the initial cut is of course what is measured. 

 By these methods Abramowitz calculated the rate of 

 regeneration in both sets of nerve-fibers and found them 

 in both instances to be about 0.5 millimeter a day. The 

 earlier determination by Parker and Porter, 0.8 milli- 

 meter a day, is not far from this more accurate figure 

 by Abramowitz, and both fall within the range of the 

 rates already published for the regeneration of nerves 

 in the frog (1.34 mm. per day, Harrison, 19 10; 0.24 mm. 

 per day, Williams, 1930; 1.44 to 0.20 mm. per day, 

 Speidel, 1933). As can be seen from these studies, the 

 degeneration of the chromatophoral nerves in Fundulus 

 begins some five days after they have been cut, and re- 

 generation is a matter of weeks later. Obviously these 

 degenerative and regenerative processes have nothing 

 to do with the formation of the caudal bands and their 

 blanching, all of which may occur in a day or so after 

 the formation of the band. Over the early period of 

 four or five days the chromatophoral nerves are func- 

 tionally active, and this activity quite reverses the older 

 conception concerning severed nerves. After they are 



