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. 
11), 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. 
