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KINETIC HORMONES — I 



3.21 CHROMATOPHORES WITH MUSCLES 



Cephalopoda. This type of chromatophore occurs only in 

 cephalopods, and forms a convenient link between those muscular 

 structures which have been considered in the previous section, 

 and the chromatophores with movable granules which follow. 



Fig. 3-9. Chromatophores with muscles from a cephalopod, 

 Loligo; on the left the muscles are relaxed and the chromatophore 

 cell is elastically contracted so that it looks pale, with the pigment 

 in a small mass at the centre; on the right the muscles have con- 

 tracted and stretched the cell body to which they are attached so 

 that the chromatophore shows the maximum amount of colour 

 (from Bozler, 1928). 



The cephalopod chromatophore (Fig. 3-9) consists of a central 

 pigment-containing cell with a highly elastic wall, and from 4-24 

 single muscle fibres, attached radially around the circumference ; 

 when the fibres all contract, they increase the area of exposed 

 pigment. Contraction of muscles, therefore, corresponds to ex- 

 pansion of the pigment and a darkening in appearance of the 

 animal. Although each muscle fibre is under direct nerve control, 

 the fibres to any one chromatophore usually contract together; 

 but adjacent chromatophores can be separately stimulated to 

 produce the very rapid and varied patterns of colour change 

 which are characteristic of cephalopods and appear to be connected 

 with their emotional states, as well as related to the colour of their 

 environment. 



