46 



COLOR CHANGES IN ANIMALS 



band on a pale Fundulus has become about as pale as 

 the rest of the fish, the animal may be placed on a black 

 background, whereupon it will darken after a few min- 

 utes in all parts except the band. This will remain pale 

 for some time, but will in the course of several hours 

 gradually darken till finally it is as dark as the rest of 

 the fish. Such procedure may be repeated back and 

 forth many times, the fish 

 blanching or darkening quickly, 

 and the band following the 

 general tint of the fish, but 

 always with a lag of some hours. 

 A situation of this kind is 

 clearly explicable on the as- 

 sumption of two sets of neuro- 

 humors, one dispersing, the 

 other concentrating, and each 

 produced by its appropriate 

 nerve endings. 



Evidence for the lateral spread 

 of the dispersing neurohumor 

 can be seen in certain experi- 

 ments that are better carried out 

 on the tail of the catfish, Amei- 

 urus, than on that of Fundulus. 

 The tail of the catfish presents 

 much the same conditions as that of Fundulus. If 

 one of its fin-rays is cut, a dark caudal band results 

 much as in the killifish. This band will likewise blanch 

 (Fig. 33) if the catfish is kept in a white environment, 

 though the process is slower than it is in Fundulus. If 

 now in a catfish with a pale caudal band two new dark 

 bands are made by cutting the fin-rays adjacent to that 

 of the pale band, and the cuts for the new bands are 

 made not near the root of the tail as that for the pale 



Fig. t ) i ) . Diagram of 

 the caudal fin of a hy- 

 pophysectomized catfish, 

 AtJieiurus, in the dark 

 phase. Above is a faded 

 caudal band and below a 

 dark newly excited one. 

 Parker, Jour. Exp. Zool., 

 1934, 69, pi. 2, fig. 6. 



