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ANNUAL REPORT SMITHSONIAN INSTITUTION, 1963 



of a different color. Where the pigment is contained in living chro- 

 matophores it may be destroyed or replaced by fresh pigments. 

 Both these processes are classed as morphogenetic color change. The 

 pigment in our own skin is located largely in chromatophores, which 

 are known as melanophores since they contain the brown pigment 

 melanin. The granules of melanin are not free to move about in 

 any systematic way in these chromatophores, which remain fixed in 

 outline, and any color change can take place only by an alteration in 

 the amount of melanin present. 



Superficially similar chromatophores are found in fish and chame- 

 leons, shrimps, and prawns, where the pattern of the integument is 

 made up of black or brown melanophores, red erythrophores, and yel- 

 low xanthophores. But unlike the mammalian chromatophores the 

 distribution of pigment granules within them is mider precise control. 

 The outline of the chromatophore is fixed, consisting of a central 

 reservoir from wliich small channels — the chromorrhizae — radiate 

 outward branching irregularly between the surrounding cells (fig. 

 1). Within these channels the pigment granules may flow about, 

 dispersing to occupy the entire network of chromorrhizae or concen- 

 trating uito the central mass as a small dot. With the pigment dis- 

 persed an area of the skin takes on the hue of the pigment concerned ; 



Figure 1. — A chromatophore of a prawn in which concentration of the pigment has 

 just begun. The pigment has withdrawn from the finest chromorrhizae, which are 

 therefore no longer visible. (Magnification, X 350.) 



