224 COLOUR IN NATURE chap.x 



presence of a green colour is frequently associated 

 with a combination of yellow and black pigments, 

 but the green colour is probably always in part 

 produced by the structure of the tissues. The 

 silvery whiteness of the lower surface of most fish, 

 and the gleaming iridescence of the other parts of 

 the body in some, are both due to the abundant 

 deposits of guanin in the skin, but the relation of 

 this reflecting tissue to the brilliant evanescent 

 colours of many tropical fishes is unknown. Spots 

 or bands produced by the irregular distribution of 

 the colouring elements are common, but the reason 

 of this irregularity of distribution is quite unknown. 

 Usually the lateral line is marked externally by a 

 distinct band of pigment, but in some cases, as in 

 Atherina presbyter, it is marked instead by a white 

 band due to a special development of reflecting 

 tissue (Cunningham). 



The colours of the lipochrome pigments vary 

 from yellow to red, but the yellows are apparently 

 the most common. In some instances the skin is 

 sufficiently transparent to allow the subjacent 

 muscles to shine through, and these may be so 

 coloured with haemoglobin as to have a distinct 

 effect upon the coloration. 



According to Mr. Beddard (^Animal Coloration^ p. 

 1 1), the green colour of the bones of the fishes 

 Belone, Protopterus, and Lepidosiren is due to the 

 presence of the mineral vivianite, but no reference is 

 given. 



