320 Professor E. B. Poulton on colocr-rclation 



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 1st 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 larvas, 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 larva; 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 larvae 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 mny be largely a question 

 of time, so that of several larvae passing the same stages in 

 given surroundings, those which grow most slowly are, on 

 the whole, the most affected. 



First Experiments with Larv^ of 

 (). bidentata (1803). 



The larvas 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 was 

 the black poplar {Po'pulus nigra). 



A careful comparison of the results of the 10 sets of 

 experiments (viz. I to IX, including Va) was made by the 

 present writer on July 6th, 1898, all the larvce being placed 

 on a background of white. At this time all except one 

 were in the last stages, and many in all the cylinders were 

 approaching maturity. Of the forms of environment made 

 use of, 7 had produced dark larva?, and 3 light. 



