LEPIDOPTEROUS PUP2E AND THEIR SURROUNDING SURFACES. 
429 
Th ese results are extremely interesting, especially as the effects of different-coloured 
light are so similar in the two species, both as to the formation of pigment and the 
production of green or other ground-colours. The effects in the former case are so 
uniform, and are so graduated in the successive colours which were used, that it is 
possible to give an approximate representation of the results by a graphic method 
making the abscissae of the scale of wave-lengths, and each ordinate of a length which 
corresponds to the average amounts of pigment obtained from all the pupae subjected 
to any one colour. Of course the results are only approximate, for there must be 
a good deal that is arbitrary in the selection of the scale of lengths to correspond 
to the different amounts of pigment in each degree of colour. The scales which were 
made use of in obtaining the averages were as follows :— 
P. rapce. 
P. brassicae. 
millimetres. 
millimetres. 
ml Deep green 1 
(3) 
14 
{) 1 Pale „ } 
5 
(2) 
28 
Light (4).j 
(1), 7 
42 
(4). 
10 
(1), h 
56 
Dark (4). 
15 
(1), « 
70 
Light (3). 
20 
(3). 
25 
Dark (3). 
30 
(2). 
40 
(1) . 
50 
Dark (1) . 
70 
In order to decide upon the points on the scale from which to draw the ordinates, 
the colours employed in the above-described experiments were examined with the 
spectroscope, and hence a test of their purity was also obtained. The tints are 
indicated on Plate 26, figs. 16-21. The results were as follows :— 
Dark-red opaque paper .— The reflected light was brightest from 60-65 on the scale 
below, the rest of the spectrum being very dim indeed, and even the chief reflected 
rays were not very bright. Hence the darkness of the tint. 
Deep-orange opaque paper .— The reflected light was brightest from 57-65, the 
yellow being especially bright; the rest of the spectrum was very dim indeed. The 
chief reflected rays were much brighter than above, and the colour of the paper was 
far more brilliant. 
Pale-yellow opaque paper. —The reflected light included a large part of the 
spectrum from 51-65, which was very bright, while the blue was reflected to a much 
less extent, and there was some more complete absorption between the blue and the 
green. 
Bright-green tissue-paper .— The transmitted light (which was almost exactly the 
same as the reflected light, differing only in intensity) which had passed through one 
layer of this paper was especially dim in the blue, and in the red to a less extent, the 
