316 Professor E. B. Poulton on colour-relation 



entirely natural conditions, larva; of the same age would 

 never be found upon the leaves or green shoots. 



It is of interest to notetliat 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 larvse 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 larvie 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 larva? 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 larvas 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 larvse were compared after 

 the winter, these same surroundings were continued in 

 each case, right up to the time when the nearly mature 

 larvse were sent to Lord Walsingham for preservation, in 

 May. The results of various comparisons point to the 

 conclusion that the larvse of G. quercifolia are not sus- 

 ceptible to the colours of the environment after the begin- 

 ning of hybernation. Thus Plate XVIII, fig. 1 represents 

 a nearly mature larva, of which the appearance before 



