the colours of certain Lepidoptera. 311 



{viz., the last). It is still possible, although unlikely, 

 that some predisposition towards either form may follow 

 from the influence of environment during the earlier 

 stages which are certainly susceptible (as will be shown 

 below). Against such a view must be set the fact that 

 both green and brown forms are found among larvae 

 which have been kept together in a muslin bag upon the 

 same branch ever since hatching, or at any rate since 

 the first stage. I have observed this several times in 

 different years. 



1889. 



The experiments in 1889 were conducted upon the 

 larvae before hybernation. I had already shown that 

 these younger larvae are certainly susceptible and capable 

 of becoming either light or dark brown, according to the 

 colours of their surroundings (Trans. Ent. Soc. Lond., 

 1888, p. 593). I was anxious to test this conclusion 

 still further. 



On July 3rd about 24 newly-hatched larvae were placed 

 in a cylinder, and fed upon filbert leaves, surrounded by 

 abundant dark twigs ; while an equal number from the 

 same batch of eggs were placed in a similar cylinder, 

 containing the leaves alone. On July 11th the two lots 

 were compared. The larvae were about 5*25 mm. long, 

 and those in dark surroundings were decidedly, but not 

 strongly, deeper in tint, some efl'ect having thus been 

 produced in about 8 days. Later on in the summer (date 

 unnoted) they were again compared, and the differences 

 were more pronounced. The larvae did not survive the 

 winter. 



It is therefore clear that these young larvae are dis- 

 tinctly susceptible during the earlier stages, when they 

 are not as yet dimorphic, but only exhibit various shades 

 of brown. 



13. ExPEKiMENTS IN 1890 UPON Phigalia pilosaria. 



38 larvae hatched in a cool cellar a few days before 

 April 26th, when they were first fed (on Populus nigra 

 and elm). The experiments did not begin until May 

 12th, when the larva3 were of an average length of 

 20 mm. in the curved position of rest. They were then 

 divided among 4 cylinders as follows : — 



