254 Experiments upon the colour-relation, &c. 
realise how surprisingly sensitive the pupe of this 
species are to surrounding influences. 
On the occasion of my taking the materials to Mr. 
Poulton, he was good enough to make a spectroscopic 
examination of the coloured papers employed, using a 
Zeiss’s microspectroscope, with an Abbé’s illuminator ; 
but although the conditions of illumination were very 
favourable, the results cannot, unfortunately, be ex- 
pressed satisfactorily in the scale of wave lengths, 
because of the large amount of white light which passed 
through the thin tissue-paper, or was reflected from its 
surface. It was clear, however, that the colour of the 
paper predominated in the spectrum, all other colours 
being relatively absorbed. 
4. Mr. Povuron’s StanparD oF THE DEGREES oF 
Cotour 1N THE Pupm or P. rapm.*—For the purpose of 
classifying the various degrees of colour assumed by the 
pupe of Pieris rape resulting from his experiments, 
Mr. Poulton established a code of grades, five in number, 
which are given in full below, with their characteristic 
features. The colours of eleven of the chief varieties 
produced by him are beautifully figured in the plate 
accompanying his paper. 
‘“*(1). The darkest forms plentifully dusted with minute 
black dots, producing a very dark grey appearance. 
There is very much pigment on the wings, and black 
patches are especially developed on the dorsal and sub- 
dorsal ridges or lines, and upon the rostrum. The 
sround colour is hardly recognisable apart from the 
grey dusting, but can be seen clearly in certain parts of 
some pup, and is then usually of a faint pinkish or 
dull yellowish tint, or some mixture of these colours. 
(2). Much less dark, due to the reduction in the 
amount of the minute dots and the black patches, which 
occur in the positions described above. Nevertheless, 
these pupe are, as a rule, of darkish grey appearance. 
The ground colour is often more clearly recognisable, 
and is generally of the same tints as above, but the 
differences between the various tints are not generally 
well-marked until (4) is reached. 
* Phil. Trans. (&e.), pp. 410, 411. 
