62 COLOR CHANGES IN ANIMALS 



medullated elements, pass out over the gray rami com- 

 municantes and the spinal nerves to their peripheral 

 effectors, smooth muscles, glands, or chromatophores. 

 These connections and their functional relations to the 

 melanophores have been recently worked out with great 

 care by Young (1933) in the dogfish Scy Ilium. Here 

 two very significant observations have been made; first, 

 that this dogfish possesses no gray rami communicantes 

 and, second, that it shows no pale areas when its integ- 

 umentary nerves are cut. This second observation is 

 in strong contrast with what has been described for 

 Mustelus by Parker and Porter (1934) and might be 

 taken as ground for doubting the correctness of their 

 statements. A repetition of their work carried out by 

 Parker (1936*3) has, however, fully confirmed their 

 findings and incidentally has led to the interesting dis- 

 covery that the spiny dogfish of the New England coast, 

 Squalus acanthias, ordinarily shows no pale bands when 

 the nerves in its fins are cut. In this respect it ap- 

 proaches Scy Ilium. It therefore seems probable that 

 the observations of Young and of Parker and Porter 

 are not really in conflict, but that different species of 

 dogfishes vary in their means of melanophore activation; 

 in some, such as Mustelus, the pale phase is under 

 nervous control; in others, such as Scy Hi urn and Squalus, 

 this phase is induced by other means. Such diversity 

 in a group of even closely related species is not surpris- 

 ing, for, as the study of animal color change progresses, 

 just such individual differences are continually appear- 

 ing. The conclusion to be drawn from this diversity is 

 that the distinction between sympathetic and para- 

 sympathetic autonomic elements which is reasonably 

 clear in the higher vertebrates is by no means so definite 

 in fishes, where individual differences may be very pro- 

 nounced. In this conclusion I am in agreement with 



