18 COLOR CHANGES IN ANIMALS 



way so that they are indistinguishable one from the 

 other. These results confirm the view held by Parker 

 and Porter that the pale phase in Mustelus is due to the 

 action on its melanophores of concentrating nerve-fibers 

 which may be stimulated by an induction current as 

 well as by being cut. 



Combining the work of Lundstrom and Bard with 

 that of Parker and Porter a reasonably clear picture of 

 the color changes in Mustelus can be outlined. This 

 fish darkens in consequence of a pituitary neurohumor 



Fig. 13. Two newly born smooth dogfishes, Mustelus; lower 

 one in the pale phase, upper one in the dark phase. Parker, Biol. 

 Bull., 1936, 70, pi. 1, fig. 1. 



carried from the pituitary gland by the blood to the 

 melanophores which are thereby induced to disperse 

 their pigment. It blanches as a result of the action of 

 concentrating nerve-fibers by methods that I shall dis- 

 cuss more fully later. 



Mustelus canis is ovoviviparous, that is, its eggs are 

 carried in the oviducts of the female till the young are 

 very fully formed when they escape from the mother's 

 body as active young fishes. A female may release from 

 four to a dozen or more such young at a time, and these 



