290 NWA TURAL VS ERENCE. APRIL, 
Nevertheless, this insect, when placed among oak leaves and twigs, 
spun a dark cocoon! Such difference in behaviour in different 
species should guard observers in future against too hasty generalisa- 
tion. 
Poulton’s recent experiments on butterfly pupz confirm the 
results given in “The Colours of Animals.” The most striking 
effects were obtained with Vanessa urtice and V.10. These chrysalids. 
vary from dark brown or black to bright golden (wrtice) or metallic 
green (io). Asin the larve, the latter effects are due to the absence 
of dark superficial pigment, and are produced by light, or bright 
metallic surrounding surfaces. As with the larve, dark surfaces lead 
to the formation of the dark pigment. The pupal colour is fixed in 
V. urtice by the surroundings of the larva when in the early stages 
preparatory to pupation, wandering in search of a suitable spot for 
attachment, or resting motionless before attachment. These stages 
are lengthened by dark surroundings, and also by disturbance ; 
Poulton believes that during them the ‘‘ colourless precursor” of the 
dark pigment which will appear in the pupa is being formed. The 
last stage of V. urtice, after the caterpillar has suspended itself, is 
not sensitive, and little or no effect is produced by changing the sur- 
roundings then; but in VY. zo this stage is longer, and some result 
can be obtained by transferring the insects to a different environment. 
Caterpillars of V. uvtice placed in a gilt cylinder in darkness 
changed to dark pupe. Dark surroundings, in a strong light, pro- 
duced slightly greater darkening of the pupe than the same environ- 
ment in the dark. Some larvae were allowed to pupate in boxes. 
lined with alternate strips of black and gold paper, so that the 
insect in its motionless stage rested partly on black and partly on 
gold. These produced pupe of an intermediate tint, but none were 
parti-coloured. As the position of the head made no difference in 
the result, it seems certain that the colour seen by the caterpillar has 
nothing to do with the effect. 
Many experiments besides simple dark and bright surroundings. 
were tried with V.70. The larvze, when exposed to blue light, pro- 
duced darkish pupz ; when placed on orange and yellow backgrounds, 
bright green pup. Chrysalids of intermediate tints were formed 
amid bright green surroundings. Dark green surroundings and red 
paper backgrounds led to dark pupe, but light falling through green 
glass, or through red glass or gelatine, made the pupe light or bright 
green. When the pupe were exposed to black ventrally, and to white 
dorsally, or vice versa, the effect of the dark surface was stronger than 
that of the white. 
The nature of the light-rays reflected from or transmitted through 
the various substances used, was tested by careful spectral analysis, 
and it appears that the presence of yellow and orange rays checks the 
formation of dark pigment, and tends to produce light, green, or bright 
larve and pupz. The difference between the results with green 
