1885.J 



Colouring of Phytophagous Larva?. 



299 



tends to produce an opposite colouration. Hence the results of the 

 experiments are as convincing as if T had been able to use the same 

 plant throughout (as I did in three cases out of the five). 



The larvae hatched July 15th — 18th, and I thought that there was 

 some difference in colour due to the food, as early as July 27th (in 

 larvae hatched July 18th and fed on 8. Viminalis), when the larvae 

 were about 15 mm. long, and advanced in the second stage. On 

 careful comparison, the backs of those feeding on 8. Viminalis, apple, 

 and crab appeared very slightly whiter green than those feeding on 

 8. Cinerea and Rubra. Before this all the larvae were yellowish-green, 

 much resembling the brighter variety. These early differences were 

 very slight, and remained so for a long time. The head and two or 

 three anterior segments were yellow-green in all the larvae up to the 

 end of the third stage, but this colour extended backwards for a less 

 distance and was less marked in the whiter varieties. While there 

 seemed to be some differences, all the larvae were of a much 

 whiter green than at first. In the third stage there was a blue 

 tinge (especially seen in those feeding on apple) about the whitish- 

 green on the backs of the whiter varieties, which became distinct 

 on placing them beside the others. The white bluish-green appears 

 on the back just above the subdorsal, and this line forms the boundary 

 between the lighter area above and the darker surface below. Some- 

 times a line along this margin, even lighter than the colour of the 

 back, indicates the position of the old subdorsal. 



There was not this sudden transition between the upper and lower 

 surfaces in the S. Rubra and 8. Cinerea larvae, although the subdorsal 

 was sometimes recognisable. The larvae feeding on crab were of 

 the lighter variety, contrary to my expectations. As the larvae ad- 

 vanced in the third stage, the differences increased and became quite 

 distinct, but they did not approach those observed upon adult larvae 

 in the field. In the fourth stage the differences still continued to 

 increase, although but slightly. The heads of the whiter varieties 

 were still yellowish. It was very noticeable now, as at all times, that 

 the apple, crab, and S. Viminalis larvae were much whiter and nearer 

 the well-known variety than the 8. Rubra and Cinerea larvae were 

 yellow-green, like the other variety. Furthermore, the 8. Rubra larvae 

 were rather yellower than those feeding on 8. Cinerea. Towards the 

 end of the fourth stage the whiter larvae (except those on S. Vimina- 

 lis) had become as white as those adult ones commonly found upon 

 apple, and exactly resembled them in colour. On the other hand, the 

 S. Rubra and especially the S. Cinerea larvae were far from resembling 

 the yellowish-green variety usually found on these plants, although 

 very different from the larvae upon apple, &c. The same facts were 

 true of the last stage (fifth) . The 8. Rubra larvae were the yellowest 

 green, and as the effect of the apple, &c, had been so much stronger 



