410 MR. E. B. POULTON ON THE COLOUR-RELATION BETWEEN EXPOSED 
supra-spiracular ridge and line are of this latter colour. The wings and under-side are 
pale transparent yellowish-white, with very small pigment patches. 
The differences between the ground-colours of (1), (2), and (3) are veiy well- 
marked, whereas the predominant grey often masks the differences between the ground¬ 
colours of (a), (/3), and (y). 
It is similarly necessary to construct a standard of the colours met with in 
P. rapes. The colours of 10 of the chief varieties are figured in Plate 26, 
figs. 32-41, X 2, and in fig. 31, natural size. 
(1) The darkest forms are 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 ground-colour is hardly recognisable apart from the grey dusting, 
but can be seen clearly in certain parts of some pupae, 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 
pupae 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. 
(3) Still lighter, but with sufficient of the grey dusting to obscure the tint of the 
ground-colour and to produce a grey or light-grey appearance. The black patches 
still occur in the same positions, but they are smaller; the same ground-colours are 
recognisable. 
(4) Very light, with little or almost none of the grey dusting, so that the ground¬ 
colour is predominant in producing the general appearance. The black spots and 
patches are very slightly developed, and sometimes entirely absent, except for a few 
black points on the side of the rostrum, which is the last position in which traces 
of the pigment patches are retained. It is, however, common to find a slight, but 
distinct, speckling due to minute black points, but not sufficiently numerous to com¬ 
bine with the lighter ground-tint and produce a grey result. The ground-colours are 
much more distinct, as they are not dimmed, and are generally pinkish, yellowish, or 
faint greenish, or some combination of these. The latter colour is transitional into 
the brighter tints of the next degree. 
(5) In certain pupse the green ground-colour is sufficiently distinct to warrant their 
classification as a separate degree. All varieties of colour are met with, from the faint, 
scarcely perceptible, yellowish-green tinge of certain pupae in the last degree to the 
more distinct and bright yellow greens arranged under this head, and finally up to a 
magnificent transparent emerald-green, which forms the culmination of the develop¬ 
ment of this tint as a ground-colour. There are also dull greens, and sometimes these 
pupae are dusted with grey spots and have the black markings developed to a 
