48 



COLOR CHANGES IN ANIMALS 



case pigment concentration and in the other pigment 

 dispersion (Mills, 1932^). 



It is no easy task to ascertain the nature of these 

 neurohumoral substances in Fundulus. Attempts to 

 extract them from the skin of this fish have failed, prob- 

 ably because they are so much involved in the scales 

 that it is impossible to bring solvents easily into close 

 contact with them. This, how- 

 ever, is not true of all fishes. 

 In some, as will be shown pres- 

 ently, they have probably been 

 in a measure isolated. One 

 point concerning their nature 

 in Fundulus seems to be clear, 

 namely, that they are not 

 carried in the blood. As al- 

 ready stated, the defibrinated 

 blood of a pale Fundulus has 

 no effect on the tint of a dark 

 fish and vice versa. This in- 

 dicates that these particular 

 neurohumors are not soluble 

 in water. If they are not open 

 to aqueous solution the only 

 other probable means of dis- 

 solving them is oil or fat, and it 

 is my opinion that these neuro- 

 humors are oil-soluble (Parker, 1933^, 1933^) an d are 

 transmitted, not through the lymph or other watery 

 fluids between cells, but from cell to cell by means of 

 their lipoid or oily constituents. Under such circum- 

 stances transmission would be slow, as in fact it is known 

 to be, and would be limited to tissues in which the cells 

 are more or less in contact with one another. In this 

 respect the melanophores of Fundulus are a favorable 



Fig. 35. Diagram of 

 the caudal fin of a catfish 

 with a normal inner- 

 vated band between two 

 newly cut dark half- 

 bands. The intermedi- 

 ate band retains its pale 

 tint throughout its whole 

 length. Parker, Jour. 

 Exp. Zool., 1934, 69, pi. 

 2, %. 7- 



