256 BONY FISHES ix. 9 



chromatophores, and of these with the iridocytes to produce inter- 

 ference effects, a wide range of colour is produced. Thus by mixing 

 yellow and black either brown or green is produced. Blue is usually 

 an interference colour. 



The use of the colour by the fish may be classified, according to the 

 scheme introduced by Poulton, as cryptic or concealing, sematic or 

 warning patterns, and epigamic or sex coloration. Cryptic coloration 









TpT Black chromabophore 

 ^pa Yellow chroma tophore 

 o Iridocyte 



Fig. 152. Coloration elements in the skin of the upper side of 

 a flounder (Platichthys). (After Norman.) 



may be achieved in various ways and may be subdivided into two 

 main types: (1) assimilation with the background, (2) breaking up the 

 outline of the fish. Assimilation is common, but is often associated 

 with some degree of disruption of outline. The absence of all pig- 

 mentation in pelagic fishes, for instance the Leptocephalus larvae of 

 eels, is an example of assimilation. Fishes living among weeds, such 

 as the sea-horses and pipe-fishes, or Lophius the angler, often resemble 

 the weeds in colour, and in addition develop 'leaf-like' processes. 

 The colour of many familiar fishes, such as the green of the tench, 

 may be said to resemble that of the surroundings by assimilation. 

 When we consider the much more numerous examples of patterns 

 involving several colours the distinction between assimilation and dis- 

 ruption is more difficult to draw. Many free-swimming pelagic fishes 

 have the upper side dark and striped with green or blue, whereas the 

 under-side is white, the beautiful pattern that is seen in the mackerel 

 (Scombei). This gives them protection from above and below, the 



