594 Comparative Animcd Physiology 



ceans possess within their chromatophores white, red, yellow, and often also 

 black, brown, and blue pigments. By appropriate rearrangements of the in- 

 dividual pigments within the chromatophores many crustaceans are able to 

 approximate rather closely the colors of the backgrounds on which they come 

 to lie. 



Although it was believed by all the early investigators that the chromato- 

 phores were controlled by nerves, there was never any satisfactory demon- 

 stration of nerve terminations at the chromatophores, nor did nerve transec- 

 tion ever appear to interfere direcdy with the responses of the chromato- 

 phores within the animal. Koller,**^- ^^ working with Crago vulgaris, pro- 

 vided the first clear evidence that a blood-borne agent was active in con- 

 trolling the chromatophores. He found that transfusion of blood from a 

 specimen darkened on a black background into a light animal kept on a white 

 background would cause darkening of the light animal. No evidence for a 

 Hghtening factor was obtained, however, by the reciprocal transfusion. He 

 also observed that blood from a yellow-adapted specimen would render yel- 

 low a white-adapted specimen. 



Perkins^^* discovered that, although denervation of an area of the body of 

 Palaemonetes in no way interfered with the responses of the region when 

 the animal was placed on a black or white background, occlusion of the blood 

 supply to any region resulted in an immediate cessation in the responses of 

 that region. Readmission of blood to the region quickly resulted in a darken- 

 ing or lightening of the region, to harmonize with the color of the remainder 

 of the body. These results were interpreted to indicate that factors for dark- 

 pigment dispersion and concentration were conveyed to the individual 

 chromatophores by way of the blood. Extraction and injection of various 

 parts of the body showed that the eyestalks were found to contain a potent 

 factor for concentrating the predominant red pigment and dispersing the 

 white^^^ in Palaemonetes and hence for blanching the animal. Removal of 

 the eyestalks results in a permanently darkened condition of the animal. 

 These results obtained by Perkins were quickly confirmed in their general 

 principles by Koller,^^ working with Crago, Leander, and Processa. The hor- 

 monal substance involved was shown by reciprocal injection experiments to 

 be neither species-specific nor genus-specific. Since these pioneering efforts, 

 numerous investigators have shown that either the eyestalks or, in a few spe- 

 cies, the anterior thoracic region contains the source of a material influencing 

 the state of the chromatophores. 



Decapod crustaceans which have been investigated extensively with re- 

 spect to their eyestalk hormonal activities in color changes appear to fall rath- 

 er naturally into three groups with respect to roles of the stalks in their 

 chromatics (Fig. 262). Group I contains such genera as Palaemonetes, Pe- 

 naeus, Hiffolyte, Leander, and Camharus. Their chromatophore systems 

 usually contain red, yellow, blue, and white pigments. Group II includes 

 only the genus Crago, which has a complex pigmentary system with no less 

 than eight diff^erently responding chromatophore types, enabling the shrimp 

 to show not only general shade and tint changes, but also a certain degree 

 of change in color-pattern. The chromatophores contain black, brown, red, 

 yellow, and white pigments. Group III includes all those true crabs (brachy- 

 urans) which have been investigated. The best known of these is the fiddler 



