1878.] Colouration of the Organic World. 49 
colouring principles,* — cyanophyll, which is blue, and xan- 
thophyll, which is yellow, — the latter of these colours being 
much more permanent than the other. Hence if, as appears 
exceedingly probable, chlorophyll is assimilated by leaf- 
eating inserts, a number of phenomena connected with their 
colouration become at once intelligible. We have mentioned 
in an earlier part of this paper that among animal tints 
pigment-greens are generally the first to fade, and that they 
become a dull yellow or a yellowish drab, as maybe observed 
in a specimen, say, of Cassida equestris, which, however care- 
fully preserved, soon loses its pale green hue, and turns 
yellowish. The reason of this change, we contend, is that 
the cyanophyll or blue colouring-matter first undergoes 
decomposition, while the yellow xanthophyll alone remains. 
A similar change, taking place in the living animal in its 
pupa condition, is the cause why pigment-greens are so rare 
alike among Lepidoptera and Coleoptera, whilst yellows and 
browns of different shades are so exceedingly common, and 
relatively so permanent. We find also that certain cater- 
pillars, green in the earlier part of their life generally, though 
not invariably, take a brown colour as they approach the 
time of their assuming the pupa state. 
But even supposing that chlorophyll is demonstrably assi- 
milated or deposited in the tissues of certain insedts, the 
hypothesis we have been suggesting takes us but a very 
little way. We have still to ask why the green colour in 
certain species remains undecomposed to the mature condi- 
tion, whilst in others it disappears in the pupal or even in 
the larval state, and how, after disappearance or absence in 
the larva, as in Chcerocampa Elpenor , it appears in the perfedt 
insedt ? We have to enquire why certain diurnal caterpil- 
lars, consuming as much chlorophyll as do any others, — e.g. 9 
Vanessa lo, V. xanthomelas, V. urticce, &c., — are free from a 
green colouration ? At the same time we must admit that 
in caterpillars of this class a yellow pattern is very rarely 
absent, as if the xanthophyll had already been separated 
from the cyanophyll. We have to explain the pigment- 
blues, of which there seem to be two, if not three, the iden- 
tity of which with cyanophyll must not he too rashly 
assumed, though in many cases we see both blue and yellow 
spots appearing in a butterfly, as if the two colours, which 
in its earlier state had been blended together, were now 
* Some authorities consider that chlorophyll is a mixture not of two, but 
of three colouring principles (Fremy and Cloez), or of four (Stokes). As 
these, however, are in all cases found to be respectively blue and yellow, the 
view we have taken will not be affeCted by these discordant results. 
VOL. VIII. (N.S.) E 
