364 Professor E. B. Poulton on colour-relation 
July 12th. The 2 last larvee had forced their way through 
the hole in the plate and were drowned. Their appearance 
had not changed, and it is probable that they had become 
mature and began to wander. 
CONCLUSIONS. 
In the final result we probably see the full and char- 
acteristic effect of the black twigs unmodified by the green 
environment in which the two youngest stages were 
passed. 
B?. A. betularia. 
May 25th, Fifteen betularia larvee transferred from green 
to black; all changing the 3rd skin and 140 mm. long. 
Some were becoming greenish, but most were brown, 
May 29th. Allexamined: the colour varied very greatly, 
but none were altogether green although there was much 
green ground- colour on some. All were in the 4th stage ; 
1 only on the black twigs and that happened to be a 
particularly green one. Many light brown and many dark 
brown 
June 2nd. Five on twigs, 3 in the 5th stage, 1 chang- 
ing 4th skin, and 1 nearly at end of 4th ‘stage. The 
latter and 1 in the 5th stage dark greenish- -brown, the 
remaining 3 very dark brown. On the leaves and green 
stems there were in the 5th stage, | green, 3 light brownish- 
green, and 2 ight brown (1 slightly greenish); in the 4th 
stage, 2. brownish-green and 2 medium brown. 
June 5th. On the black twigs there were 8 larvae, 7 in 
the 5th stage (8 of them changing the 5th skin), 5 dark 
brown, | bright green (changing skin), and 1 brownish- 
green (half-grown in stage); 1 im 4th stage and brownish- 
green. On the light brown stem of P. nigra was a single 
larva which harmonized with it very exactly. On the 
leaves were 5 larve, 2 small in the 5th stage and light 
brown, 3 in the 4th, 1 dark (changmg the 4th skin), u 
brownish- green, and 1 greenish-brown. 
June 14th. Six larve in the 6th stage were on the 
twigs and very deep black, some of them with a small 
amount of greyish markings. One similar larva on 
green: 1 larva in the 6th “stage on green was of a 
uniform dull light grey tint: of 2 larvee in the 5th stage, 
1 was changing the 5th skin and hght brown overspread 
