214 Colour of cocoons, piipce, and larva. 



It is scarcely necessary to describe the course of the 

 experiment in detail, as Mr. Poulton has already done 

 so ; but I may give the conditions seen at two examina- 

 tions : — 



24th July. Lot A. Originally 13. Of these 8 were 

 of the full bright green colour, 2 were brown- 

 green, and 2 were brown. 



Lot B. Originally 14. Of these 12 were very dark 

 in colour, 1 was green, and 1 was dead. 



I then took all the sticks out from among the B lot, 

 and put them with Lot A. On the 7th of August the 

 result was as follows : — 



Lot A. 7 very green, 2 medium brownish green, 

 1 darker, but not of the full dark colour ; 2 dead. 

 Lot B. 12 still very dark, 1 green as before. 

 No further change in colour took place, so far as I could 

 judge. The effect therefore, once produced, seems not 

 to be reversible, as it is in the case of the sole and the 

 like. The change of colour is, as Poulton says, pro- 

 duced by the deposit of dark pigment in the one set of 

 larvse, and by the absence of it in the other. 



It should be mentioned that these larvae, like many 

 other Geometrce, are almost exclusively night-feeders, 

 and rarely move by day. Those provided with black 

 sticks sat eitlier on them or on the green twigs of their 

 food throughout the day. Of course, in this case the 

 resemblance to sticks in the one case and to green 

 twigs in the other is unquestionable, and I think it may 

 be fairly argued that this resemblance may contribute 

 to the protection of the animal. 



My best thanks are due to Mr. Poulton for giving me 

 an opportunity oi making this experiment, which I have 

 watched with great interest. 



