24 COLOR CHANGES IN ANIMALS 



the fin membrane (Fig. 18). This mark can be seen in 

 the males from April to November, but not at other 

 times of year (Parker and Brower, 1935). Such sea- 

 sonal markings and the accentuated color changes that 

 accompany them during the breeding season undoubt- 

 edly play an important role in the sporting of the sexes 

 in mating. The less pronounced year-round changes of 

 darkening and blanching are probably of a character 

 purely protective. 



Some of the observations recorded in the preceding 

 paragraphs are not of great moment for the present 

 discussion and have been little studied, but I have intro- 

 duced them here that you may appreciate to some extent 

 the complexity in the reactions of the melanophores in 

 the killifish, and that you may have some understanding 

 of what we are dealing with when we attack the prob- 

 lem of even the simpler color changes in this fish. The 

 main features to be kept in mind in the following dis- 

 cussion are that in Fundulus under normal conditions 

 the animal turns quickly dark in an illuminated, black 

 environment, and less quickly pale in a similar white 

 one. It is hardly necessary to say that the dark phase 

 of the fish is one in which the pigment of its melano- 

 phores is fully dispersed, and the pale phase one in which 

 this coloring matter is compactly concentrated. 



We may now proceed to inquire into the mechanism 

 of the melanophore changes in Fundulus and, since they 

 are dependent upon the eyes, we are naturally led to 

 ask first of all how much of a part nerves play in these 

 reactions. A host of investigators have attempted to 

 identify chromatophoral nerves by the very reasonable 

 step of cutting given nerve-strands and then looking for 

 possible color changes in the integumentary areas that 

 have been thus denervated. This method was em- 

 ployed by Briicke, by Pouchet, by von Frisch, and many 



