on colour-relation. 221 



July 19th. — I drew one of the largest larvre. This 

 lavva (figured m PI. XL, fig. 4) was the darkest I 

 obtained, and measured 7^ cm. in length. By this time 

 all the six larvae were very dark, that is, darker than 

 the darkest of those with green or white surroundings. 

 The whole ground colour of the body was a clear brown, 

 not brownish merely or brownish grey ; the two wavy 

 dorsal lines were broadly and distinctly marked in very 

 dark brown in one larva, and less darldy but distinctly 

 in the other five. The head and dorsal humps were 

 tawny, outlined and marked with black. 



From the time of the last ecdysis, the larvae had been 

 showing signs of unhealthiness, and now they died oft" 

 one by one. By Aug. 3rd only one was left — the darkest 

 — and this larva died on Aug. 6th. I was not able to 

 discover the cause of death, and up to this time they 

 bad fed as usual, and seemed to thrive well. 



Total results of the foregoing experiment : — 



Colour. No. of larv;!?. 



Dark brown (dorsal lines very dark) ... ... 1 



Brown (dorsal lines distinct, but not so dark) ... 5 



Total 6 



Ci/Under 12. — June 25th. — I put six larvae (hatched on 

 one day) in the second stage into cylinder 12, and gave 

 black sticks with the food-plant {Salix vitellina). Up to 

 this time they had had leaves without sticks or attention 

 to the colour of the leaves. 



July 4th — The second ecdysis took place. 



July 7th. — With this set I was using the plan adopted 

 by Mr. Poulton in some of bis earlier experiments, viz., 

 that of surrounding the cylinder with tissue-paper of the 

 shade required, with a view to deepening the effect. On 

 this day I applied brown tissue-paper to the cylinder 

 containing the larvae, and placed it in a strong light, as 

 otherwise the paper made the cylinder almost dark. 



July yth. — Acting on advice from Mr. Poulton, under 

 whose kind direction I was working, I removed the 

 tissue-paper, as he had come to the conclusion that the 

 shadow caused by it rather hindered than increased the 

 effect of the surroundings. At this time the length of 

 the largest larva, fully stretched, was G|- cm., and that 

 of the smallest nearly 5 cm. A darkening of colour had 



