Ordinary food-plant. 



Upon birch leaves 

 and twigs (including 

 dark ones) for the whole 

 larval life up to Aug. 

 18, and retained to the 

 end in many cases. 



Aug. 18. — Compared. 



A. Greyish brown . 1 

 Greenish brown . 1 

 Eeddish brown . 3 



B. Beddish brown 4 

 Greenish brown . 1 

 Greyish brown . 2 

 Greenish . . . 1 



C. Light greenish 

 brown . . . 1 



Brown .... 4 



D. Beddish brown 1 

 Greenish brown . 2 



21 

 Many removed for 

 other experiments. 



Sept. 3. — All the 8 

 remaining larvae in last 

 stage, most being near- 

 ly mature, the smallest 

 about half through the 

 stage ; 4 green, although 

 not very bright, brown 

 dorsal line present ; 1 

 dull greenish brown ; 3 

 dull reddish brown. 

 The last 4 were not 

 very dark. 



La. 



Dark twigs. 



In feeding the larvae 

 it is probable that twigs 

 with a great profusion 

 of leaves were em- 

 ployed ; hence the ab- 

 sence of very dark 

 forms and the preva- 

 lence of green. 



In I. up to Aug. 

 18, then dark haw- 

 thorn twigs inter- 

 mixed with food. 



Aug. 18.— 4 of the 

 B larvaj (2 reddish 

 brown, 1 greenish, 

 and 1 greyish brown, 

 the lighter of the 2), 

 3 of the C (2 brown 

 and the lighter onei, 

 and 1 of the D (the 

 lighter of the 2 green- 

 ish brown ones) were 

 introduced from I. 

 at this date. 



Lb. 

 Blinding Experiment. 



Sept. 3.— 1 a de- 

 cided green, much 

 brighter than any in 

 I. ; 4 very dark 

 smoky brown, much 

 darker than the red- 

 dish brown ones in 

 I. ; 1 greyish brown, 

 much darker than 

 the greenish brown 

 larva in I. 1 of the 

 dark larvas pupating. 



The effect of the 

 dark twigs jDresent 

 between Aug. 18 and 

 Sept. 3 is very clear 

 on all the larva;, ex- 

 cept the single bright 

 green one, which 

 seems to have been 

 especially predis- 

 posed towards this 

 variety, or more pro- 

 bably may have been 

 older than the others 

 and its colour already 

 determined. 



In I. up to Aug. 18, 

 then surrounded by 

 green twigs and leaves 

 of birch, 3 out of 5 

 larvffi being blinded. 



Aug. 18.— The A lot 

 from I. introduced at 

 this date. By Aug. 21 

 they had changed their 

 last skins, and some 

 were blinded, as fol- 

 lows : — 

 1 light reddish brown 



{blinded). 

 1 light reddish brown 

 (unbllnded). 

 1 dark reddish brown 

 {unhlhided). 

 1 greenish brown 



(blinded). 

 1 greyish brown 

 (blinded). 



Sept. 3. — The larvffi 

 had a very smoky ap- 

 pearance, especially 

 the blinded ones ; the 

 others redder and not 

 so dark as those in I. a. 



XL 



Green and brown 

 leaves. 



The results are not 

 convincing, because 

 the larvae were only 

 subjected to these con- 

 ditions during the last 

 stage ; and more care- 

 ful recent work (1892) 

 shows that they are but 

 little sensitive during 

 this period. Neverthe- 

 less, the results are 

 such as to suggest fur 

 ther blinding experi- 

 ments in the future, 

 and for longer periods 

 of larval life. 



Surrounded for about 

 a fortnight with the 

 leaves alone of birch, 

 but these had become 

 old and brown towards 

 end of time. 



Aug. 18. — Compared. 

 A 



B. Greenish . . 1 

 Light greenish 



brown ... 2 

 Dark reddish brown 2 



C. Beddish brown 3 



D. Eeddish brown 5 



13 



3 of theB (1 of each 

 colour), 1 of the C, and 

 2 D (changing last skin 

 but one) removed to 

 dark surroundings 

 (II. a). Fresh green 

 leaves added and brown 

 removed. On Aug. 21 

 an escaped reddish 

 brown larva (D) was 

 added. 



Sept. 15. — 1 pupa, 8 

 nearly mature green 

 larvffi with brown dor- 

 sal line. 



The eiJect of green 

 surroundings predomi- 

 nated in spite of the 

 leaves becoming brown 

 part of the time. This 

 result and that of I. 

 perhaps indicates that 

 the larvffi may have 

 been somewhat pre- 

 disposed towards the 

 green forms. 



