the colours of certain Lepidoptcra. 389 



The percentages of ^, 0, *, ^, and /x depend on such 

 small totals that they are not of much value. The 

 remaining figures are mostly trustworthy, and lead to 

 some interesting conclusions. 



The comparison of « with /?, and of a with ^, entirely 

 confirm the conclusion at which I arrived in 1886,— that 

 crowding the larvfe tends to produce dark pup?e, the 

 effect being presumably due to the influence upon each 

 larva of the dark skins of its neighbours. 



Any supposed chemical influence of the surface is 

 entirely dispelled by the comparison. When the same 

 material is employed in different forms, different effects 

 maybe produced if the character of the reflected light is 

 altered thereby. Thus Dutch metal produces least effect 

 when it possesses a very highly polished surface (e and 0, 

 most when it is broken up by a small raised pattern, as 

 in « (/? shows the effects of crowding to a remarkable 

 extent), while the Dutch leaf, which is not highly 

 polished, but of a very bright golden appearance, also 

 produces powerful effects (7). It is probable, indeed, 

 that this latter is the most powerful form of the sub- 

 stance, for the averages of 1886 are brought down by 

 the inclusion of pupae which were excluded or separated 

 in 1888 (pupse on the floors or food-plant of cases, and 

 crowded pupae). 



So, too, the silver paper produced far more effect when 

 in strong light (>j, 6) than when the light was somewhat 

 dim 0, ^), and bright tin-plate (^), although the numbers 

 were very small, is evidently far more powerful than the 

 duller, greyer surface of tin-paper. 



In 1886 I had sometimes thought that the pupae pro- 

 duced on white opal glass tended to be silvery rather 

 than golden, and one object I had in view was to test 

 for any such susceptibility. This was the chief reason 

 for employing the silver and tin surfaces. The results 

 were entirely negative. Single pupae belonging to (5)s 

 or (4)s are occasionally met with having a silvery instead 

 of a golden lustre, but there was no evidence that they 

 were commoner on the surfaces with a corresponding 

 colour. The tendency of silvery surfaces is in the same 

 direction as that of golden ones, only it is not equally 

 powerful. 



