86 KINETIC HORMONES — I 



extended by the second, or pharmacological, form of investigation, 

 using injections of organ-extracts and purified hormones. The 

 second method has been that chiefly exploited in the search for 

 crustacean hormones by Brown and his co-workers in America; 

 they inject extracts of suspected endocrine organs into variously 

 prepared animals, for which environmental changes are as far as 

 possible ruled out. This method can eventually lead to the location 

 of the source of the hormones, and since about 1942 it has been 

 shown (Brown, 1944), for a steadily increasing variety of pigment 

 cells with moving granules, that two hormones are in control 

 (Table 9), although, for technical reasons, one is usually easier 

 to demonstrate than the other. This, perhaps, accounts in part for 

 the controversy which centred for so long around the problem of 

 whether or not a second antagonistic hormone was necessary to 

 account for crustacean colour change, or whether all the observed 

 changes in any given animal could be accounted for by quantitative 

 differences in a single hormone (Parker, 1948). 



The following account of the reactions of chromatophores and 

 their control by hormones in Arthropoda and Vertebrata is only 

 limited to red, white and black pigments in order to simplify the 

 picture (Table 9) ; this is perhaps to oversimplify it, but it should 

 suffice to give a frame of reference within which to consider 

 further data, such as those relating to the complex system in 

 Leander (Carlisle and Knowles, 1959). Much more information is 

 still needed to extend the knowledge of most species from the 

 realm of mere pharmacology towards an understanding of their 

 natural physiology. 



Red pigment in chromatophores 



Crustacea. Physiological colour change in Crustacea is rela- 

 tively slow in reaching equilibrium; but it can bring about an 

 almost complete reversal of the state of some chromatophores in 

 two or three hours. For instance, the following observations can 

 be made on the red chromatophores of Palaemonetes, or of the 

 fiddler crab, Uca (Figs. 3-15 and 3-19), if in the latter case it is 

 remembered that the animals show a diurnal rhythm of colour 

 change in daylight, so that observations must all be made over the 

 same few hours of the day. One group of animals can be adapted 



