94 KINETIC^HORMONES — I 



dispersion is reduced, by reversal of day and night illumination 

 (Webb, Bennett and Brown, 1954). 



Vertebrata. Relatively little is known of the control of red 

 pigment in vertebrates. 



Teleostei. The red (and also the yellow) chromatophores of 

 the minnow, Phoxinus, appear to be under purely hormonal con- 

 trol and to show the usual background responses. The dispersing 

 action of intermedin, B, from the pars intermedia (§ 2.123), is 

 well established (Giersberg, 1930 and 1932), but the source of 

 a red-concentrating hormone has only been rather uncertainly 

 located in the epiphysis or pineal organ. Adrenaline has no effect. 

 Other red pigment cells of fish, such as Holocentrus, are controlled 

 by nerves only. 



Reptilia. The erythrophores of the chameleon, Lophosauray are 

 probably under nerve control, like their melanophores, but they 

 do not seem to have been fully investigated (Brown, 1950«). 



White pigment in chromatophores 



Crustacea. The hormonal control of other pigments in 

 chromatophores is essentially similar to that already described for 

 red pigments, though many minor variations have been found 

 (such as those between Palaemonetes and Crago)^ and much 

 remains unknown (Tables 10 and 11). 



In bright light on a white background the response of guano- 

 phores is usually dispersion of their white pigments, which 

 reinforces the pallor produced by the concentration of dark pig- 

 ments in the other chromatophores. In all the Decapoda exam- 

 ined (except the Brachyura), the richest source of extracts which 

 induce these light-adaptations is the sinus gland, and this is 

 almost certainly the organ where the natural hormones are liber- 

 ated into the blood; for eyestalk (and therefore sinus gland) 

 removal causes the opposite effect. Like the natural response to 

 an illuminated black background, it results in the white pigment 

 becoming concentrated and the dark pigments being dispersed. 

 Extracts causing the latter effects can usually be obtained from the 

 commissures (which include circumoesophageal connectives and 

 tritocerebral commissures) ; but it is not known for certain at what 

 point the natural hormone passes into the blood. 



