144 
COLOUR IN NATURE 
CHAP. 
considerable evidence to show that yellow, green, 
and brown ground-colours in vegetarian larvae are 
all due to pigments derived from the food. The 
pigments frequently colour the blood very markedly; 
it will be recollected that the blood in insects has 
probably no connection with respiration, but is 
haemolymph, primarily concerned with nutrition. 
The blood of the pupae and adults is often likewise 
green and coloured with these derived pigments, 
but as yet there seems to be no instance described 
in butterflies or moths in which these pigments 
assist in coloration (a possible exception will be 
discussed when we consider butterflies). They are 
retained within the body, however, and not in¬ 
frequently colour the eggs and thus the newly- 
hatched larvae. The break between larval and 
adult coloration seems in Lepidoptera to be complete. 
But lipochrome pigments at least are not always 
absent in adult insects, for Zopf describes red and 
yellow pigments belonging to this group in several 
small leaf-eating beetles. In Lina populi , for example, 
which lives on the leaves of the poplar, a red 
lipochrome colours the wing-covers and part of the 
abdomen, it is found in the secretion of the salivary (?) 
glands, and occurs associated with oil-drops in the 
ova. One is tempted to suppose that its presence 
here is associated with the prolongation of the larval 
diet into adult life. 
Meaning of Derived Pigments 
We must now proceed to consider what the 
abundant occurrence of derived pigments in insects 
