on colour -relation. 229 



poplar only only. The larvfe when hatched were of a 

 uniform dark colour. 



June 14th.— The first ecdysis occurred. The larvre 

 became very light green, with a row of dark spots along 

 the back. 



June 16th. — The larvae had darkened a little, but 

 showed no tendency to become brown. 



June 26th. — The largest larva became quiescent. It 

 had seemed quite healthy up to this time. 



June 29th. — The largest larva pupated, the pupa being 

 only a little over 1 cm. in length, but perfectly formed. 

 I could not assign any reason for this early pupation. 



July 2nd. — The second ecdysis took place. The row 

 of spots disappeared, but the green colour was persistent. 

 (These spots never appeared in the larvae with dark 

 surroundings.) 



July 6th. — The larvae were still all green, but paler. 



July 14th. — The third ecdysis occurred. The shade 

 of green of all the larvae became very delicate and bluish. 



July 20th. — Up to this time the food had been young 

 green shoots with green stems, but now, finding it pos- 

 sible to procure leaves with stalks long enough to use 

 singly, I gave leaves only for the rest of the time. 



July 21st. — The fourth ecdysis took place, and was 

 followed by a slight intensification of colour in all five 

 larvae. 



July 22nd. — I drew the greenest larva (PI. XL, fig. 7), 

 but, like the larvae in cylinder 2, these varied very 

 slightly in depth of colour. Their general ground colour 

 was a light and peculiarly delicate shade of bluish green ; 

 the dorsal surface was tinged with a shade of brownish 

 grey, so light as to be barely perceptible, and was mottled 

 with minute dark specks ; the heads were tawny, pen- 

 cilled with black ; the dorsal humps black-marked ; the 

 legs and claspers green, of the same shade as the body. 

 The largest larva measured nearly 7| cm. ; this was the 

 largest larva obtained in the case of this species. 



Aug. 9th. — The first larva was spinning up on the 

 floor. 



Sept. 2nd. — The second larva pupated. I saw it im- 

 mediately after pupation ; the pupa then was of a bright 

 deep shade of ^'ellowish green. It had come out from 

 its partially-spun cocoon and pupated outside. 



Sept. 3rd. — The second pupa had turned to the per- 



