COLOUR CHANGES 517 



lated by the nervous system, presumably by the discharge of impulses down 

 the same axons that conduct the secretory material to the storage depots 

 (4, 9, 43). 



Various lines of evidence have shown that a multiplicity of chromato- 

 phorotropic principles is involved in the pigment-cell responses of Crus- 

 tacea. The operation of two hormonal principles in Ligia oceanica was 

 indicated by different time relations of the background responses. One 

 factor causes blanching of the body (W-factor); the other, darkening 

 (B-factor). Experimental work on decapods has involved studying the 

 effects of extirpation of eye-stalks, injection of extracts, comparison of 

 extracts on different species, and attempts to separate and purify the 

 various chromatophorotropins. 



Three physiological groups have been distinguished among higher 

 Crustacea on the basis of chromatic changes brought about by removal of 

 eye-stalks and injection of eye-stalk extracts. The first group includes many 

 isopods, mysids and reptant decapods (PaIaemon,Palaemonetes, etc.). In this 

 group removal of the sinus glands causes the dark chromatophores to 

 disperse and the body to darken. On administration of sinus-gland extract 

 the body blanches as the result of concentration of the dark pigments. 



The second group is represented by the sand shrimp Crangon. Removal 

 of the eye-stalks in Crangon is followed by temporary darkening of the tail 

 through dispersion of black and red pigments in the telson and uropods, 

 and blanching of the remainder of the body as the result of concentration 

 of the dark pigments. Injection of extracts of the sinus glands into an 

 animal shortly after removal of the eye-stalks brings about concentration 

 of the black pigment in the tail, and the whole body is consequently 

 blanched. The main action of the sinus glands, therefore, is to concentrate 

 the dark pigments and effect blanching of the animal. 



The third group includes brachyurans and some isopods. In the fiddler 

 crab Uca pugilator, removal of the eye-stalks brings about rapid blanching 

 through concentration of red and black pigments and dispersion of the 

 white pigment. Injection of sinus-gland extract into crabs from which the 

 eye-stalks have been removed causes darkening although the white pigment 

 remains dispersed. 



Brown distinguished three different chromatophorotropins in the sinus 

 gland, varying in relative concentrations or effectiveness in different groups. 

 One of these principles has a marked effect in expanding the dark chroma- 

 tophores, and is referred to as the £/ctf-darkening hormone. A second 

 factor shows a pronounced effect in concentrating the red chromatophores 

 of Palaemonetes, and is known as the PaIaemo?ietes-\ightQnmg hormone. 

 These two factors were partially isolated by treating extracts of sinus glands 

 with ethanol. By this procedure were obtained two factors : one, alcohol- 

 soluble, causing concentration of the red pigment in Palaemonetes, and 

 another, alcohol-insoluble, having a pronounced effect in causing dis- 

 persion of the black pigment in Uca. These two principles, £/c#-darkening 

 and Palemonetes-\\$\\emng, have been recognized in the sinus glands of 



