316 Professor E. B. Poulton on colowr-relation 
entirely natural conditions, larvee of the same age would 
never be found upon the leaves or green shoots. 
It is of interest to note that the larva never rested upon 
the lichen itself, but upon the bark of the sticks between 
the masses of lichen. This position is consistent with 
the larval appearance, which is that of bark partially 
grown over with lichen. 
There can be little doubt that the larva is influenced by 
the colours of the environment from the time at which it 
first seeks the older wood, but a certain period is required 
before the effects become visible. A very obvious adjust- 
ment to the three forms of environment was recorded on 
August 14th—-so obvious indeed that the first trace of a 
visible result might probably have been detected some few 
days earlier. The adjustment continued to become more 
complete right up to the beginning of hybernation. On 
Aug. 31st it was noted that the effects of the three environ- 
ments had greatly increased. On Sept. 21st a careful 
comparison of all the larvae was made upon a white paper 
background. It was then thought that the adjustment 
was as complete as it was likely to be before hybernation, 
and for many larve this conclusion was justified. In 
others however the effects continued to deepen right on 
into October, as will be seen in the complete account of 
the experiments. The latest changes probably took place 
after the larve had ceased to feed; indeed they had eaten 
very little for some time previous to October 3rd. The 
degree of cryptic adjustment to the three environments 
which had been reached by the beginning of hybernation 
can be seen by a glance at the upper part of Plate 
XVII, where examples of all the types of colouring are 
represented. 
In arranging the larve for hybernation many of the 
environments were shifted, in order to test the existence 
of any larval susceptibility during this period; and, as no 
effects were visible when the larvae were compared after 
the winter, these same surroundings were continued in 
each case, right up to the time when the nearly mature 
larvee were sent to Lord Walsingham for preservation, in 
May. The results of various comparisons point to the 
conclusion that the larve of G. quercifolia are not sus- 
ceptible to the colours of the environment after the begin- 
ning of hybernation. Thus Plate XVII, fig. 1 represents 
a nearly mature larva, of which the appearance before 
