VIII 
ORIGIN AND USES OF COLOUR IN ANIMALS 
197 
This was shown by feeding two sets of larvae on the same 
plant but exposed to differently coloured surroundings, 
obtained by sewing the leaves together, so that in one case 
only the dark upper surface, in the other the whitish under 
surface was exposed to view. The result in each case was a 
corresponding change of colour in the larvae, confirming the 
experiments on different individuals of the same batch of 
larvae which had been supplied with different food-plants or 
exposed to a different coloured light. 
An even more interesting series of experiments was made 
on the colours of pupae, which in many cases were known to 
be affected by the material on which they underwent their 
transformations. The late Mr. T. W. Wood proved, in 1867, 
that the pupae of the common cabbage butterflies (Pieris 
brassicae and P. rapae) were either light, or dark, or green, ac¬ 
cording to the coloured boxes they were kept in, or the colours 
of the fences, walls, etc., against which they were suspended. 
Mrs. Barber in South Africa found that the pupae of Papilio 
Nireus underwent a similar change, being deep green when 
attached to orange leaves of the same tint, pale yellowish-green 
when on a branch of the bottle-brush tree whose half-dried 
leaves were of this colour, and yellowish when attached to 
the wooden frame of a box. A few other observers noted 
similar phenomena, but nothing more was done till Mr. 
Poulton’s elaborate series of experiments with the larvae of 
several of our common butterflies were the means of clearing 
up several important points. He showed that the action 
of the coloured light did not affect the pupa itself but the 
larva, and that only for a limited period of time. After 
a caterpillar has done feeding it wanders about seeking a 
suitable place to undergo its transformation. When this is 
found it rests quietly for a day or two, spinning the web from 
which it is to suspend itself; and it is during this period of 
quiescence, and perhaps also the first hour or two after its 
suspension, that the action of the surrounding coloured 
surfaces determines, to a considerable extent, the colour of 
the pupa. By the application of various surrounding colours 
during this period, Mr. Poulton was able to modify the colour 
of the pupa of the common tortoise-shell butterfly from nearly 
black to pale, or to a brilliant golden; and that of Pieris rapje 
