330 MR. E. B. POULTON ON THE COLOUR-RELATION BETWEEN EXPOSED 
consisted of the least advanced larvae, very carefully selected, it follows that the 
remainder, which (with two exceptions, forming D division) formed this division, 
were comparatively mature and doubtless far advanced in Stage II. of the preparatory 
period when the black roof was added. Nevertheless the results are important 
when taken with others, as showing that the influence works upon the larva for some 
considerable tune before pupation, and therefore, when it is only introduced shortly 
before the change, great effects are not produced; but the same conclusion will be 
reached by far more careful experiments, to be described below. 
D. Two larvae were already suspended from the green glass cover alluded to above 
on the evening of the 16th. The glass was placed in a vertical position in a strong 
north light, the larvae being on the side towards the room. On comparing, their 
colours were :— 
2 pup®, both (3), 1 darkish and 1 lightish. 
Thus 31 pupae were obtained from Series III., and I do not think that any of the 
larvae died. I did not, at the time, know the number of larvae in a company of average 
size, or it would have been clear that the captured larvae were merely the remnant of a 
company of which the large majority had already sought pupation. Being greatly in 
want of material, I searched very carefully, and, I believe, obtained all the larvae left 
on the nettle-bed. Had I known that the larvae were in this position, and therefore 
almost certain to pupate directly, I should have acted differently. Further experi¬ 
ments will show that, to obtain sufficiently accurate results, the most exacting 
demands are made upon time and at a moment’s notice ; for as soon as the material 
is obtained the first few hours may prove to be the most important of all. 
Nevertheless, the conclusions from A. division are most interesting, and thoroughly 
borne out by other work; and, allowing for all sources of error, the comparison 
between A. and B. is also satisfactory. 
IY.—Another company of mature larvae was found, also on August 15, on a large 
patch of nettles in Binsey churchyard. On the evening of the 15th these were 
placed in two cylinders, one very large and covered with a sheet of clear glass, the 
other smaller and covered with a sheet of “ opal ” glass. Both were on the floor, in 
the shadow of the table. On the next day they were re-arranged according to the 
following divisions. Comparison of the pupae, together with those of all previous 
series except I., took place August 22. 
A. In the afternoon of the 16th 12 larvae were taken from the large cylinder, and 
were placed in a small cylinder (6 "2 centimetres in internal diameter ; ITS decimetres 
in height) covered with two layers of black tissue-paper, with a similar roof, also of 
two layers, and a black floor. The larvae which were selected had not yet entered 
