320 Professor E. B. Poulton on colowr-relation 
we furthermore take into account the more intense effects 
which were produced as additional stages were exposed to 
a dark environment, we may feel confident that every stage 
except the Ist and the 5th or 6th, is sensitive. These 
require further experimental testing. 
A very interesting and unlooked-for effect was produced 
in many of the transferred larvee, viz. an overspreading 
greyness or the appearance of grey patches. Thus, although 
the effect of the earlier surroundings appeared at first 
sight to be entirely obliterated, the larvae were nevertheless 
unable to develop their full and characteristic response to 
the later environment. Details will be found in the account 
of the experiments. It only remains to point out that 
experiment A! probably indicates that these larve are 
susceptible to the colours of the branches at a period when 
they are at any rate chiefly to be found upon the leaves 
and leaf-stalks, and that there was some evidence to show 
that the influence of environment may be largely a question 
of time, so that of several larvee passing the same stages in 
given surroundings, those which grow most slowly are, on 
the whole, the most affected. 
First EXPERIMENTS WITH LARV OF 
O. BIDENTATA (1893 
The larvee from the first set of eggs sent by Mr. Porritt 
from Yorkshire hatched at about the same time, so that 
nearly all the experiments recorded on pages 322—325 in 
a tabular form were started on the same day, May 22nd. 
The observations were in part conducted by Mr. Holland and 
in part by me, as is indicated by the initials or name under 
the dates in the left-hand column of the table. Hence in 
the account of each experiment there is the opportunity of 
comparing two independent sets of observations. 
The food-plant made use of in all these experiments wa 
the black poplar (Populus nigra). 
A careful comparison of the results of the 10 sets of 
experiments (viz. I to TX, mcluding VA) was made by the 
present writer on July 6th, 1893, all the larvee bemg placed 
on a background of white. At this time all except one 
were in the last stages, and many in all the cylinders were 
appro: oe maturity. Of the forms of environment made 
use of, 7 had produced dark larvae, and 3 hght. 
