the colours of certain Lepidoptera. 



309 



ExPERIMEXT I. 



Dark Surroundinos. 



ExPERUrENT II. 

 Green Surroundings. 



Aug. 19. — 7 larv;« introduced; 

 average length, 11"4 mm. Dark 

 twigs intermixed with food-plant 

 (oak). 



Aug. 24. — Older leaves of a darker 

 green were offered at this date. On 

 all other occasions, unless specially 

 noted m this and other experiments, 

 I was careful to use leaves of the 

 same age. 



Sept. 2. — Refed ; the average 

 length in both I. and II. was now 

 16-1 mm. 



Sept. 13. — The average length was 

 now 20-6 mm. The difference in 

 colour was very great. The lightest 

 of these 7 were much darker than 

 the darkest of II. These were 

 rather variable, and marked with 

 various shades of grey and brown. 

 It is true here, as in all experiments 

 with stick-like larvre, that, except 

 when feeding, they are almost in- 

 variably found resting on the twigs. 



Sept. 30. — The average length 

 was the same ; it is therefore pro- 

 bable that they had ceased feeding 

 for some little time. 



Nov. 12. — The larvae were care- 

 fully compared for the last time : 1 

 had died. The 6 larvae were various 

 shades of dark brown, with patches 

 of greenish brown often present, and 

 far darker than those of II. 



Aug. 19. — 7 similar larvae intro- 

 duced. 



Aug. 24. — Younger leaves of a 

 lighter green were offered at this 

 date. 



Sept. 2. — Also refed. The effects 

 of surroundings were already very 

 marked, the experiment having 

 lasted about a fortnight. 



Sept. 13. — The general effect of 

 the larvoB was greenish ; their colour 

 may be described as a light greenish 

 grey ; they were very slightly vari- 

 able in colour and marking. 



Sept. 80. — The difference was as 

 marked as before. 



Nov. 12. — All 7 larva? were of a 

 light greenish brown. They had 

 now been hybernating, and had not 

 been offered food for a long time. 



I bad arranged to continue the experiments through 

 the winter, some of the lightest larvae being exposed to 

 dark surroundings, and vice versa. It would be very in- 

 teresting to test whether there is any susceptibility at 

 this period when concealment is so especially necessary. 

 It is, however, improbable that any susceptibility exists 

 at this time because of the physiological inactivity of 

 hybernation. It must furthermore almost invariably 

 happen that the larvae remain resting throughout winter 

 upon surfaces with which they had previously been 

 brought into resemblance. The experiment failed, because 

 only a single larva survived the winter. This individual 

 spun a cocoon May 25th, 1889. 



