16 



COLOR CHANGES IN ANIMALS 



Fig. io. Dorsal view of a 

 pectoral fin from a dark dogfish, 

 Mustelus, showing a light band 

 in process of gradual disappear- 

 ance two days after the initiating 

 cut had been made. Parker 

 and Porter, Biol. Bull., 1934, 

 66, pi. 1, fig. 2. 



follow the courses of the 

 nerves and not those of 

 the vascular supply. 



When a pale band on 

 a dark dogfish begins 

 to disappear, it does so 

 by lateral invasion. The 

 dark area of the fin in 

 general creeps in on the 

 pale band from the two 

 sides till the band is ob- 

 literated (Fig. 10). If, 

 before this invasion of 

 the pale band has set in, a 

 longitudinal cut is made 

 along one edge of the 

 band, no invasion will occur on that side but the band 

 will gradually disappear 

 by invasion from the op- 

 posite side and from that 

 side only (Fig. 11). This 

 condition suggests that 

 the disappearance of pale 

 bands results from the 

 lateral infiltration of 

 some darkening agent. 

 At least there is no evi- 

 dence of any other fac- 

 tor being involved, for a 

 cut made in a pale fish 

 is never under any cir- 

 cumstances followed by 

 the formation of a dark 

 band or any other such 

 change. 



Fig. 11. Dorsal view of a 

 pectoral fin from a dark dogfish, 

 Mustelus, showing a light band 

 in process of disappearance, an 

 operation here locally checked 

 by a longitudinal cut on one 

 side of the band. Parker and 

 Porter, Biol. Bull., 1934, 66, pi. 

 1, fig- 3- 



