the colours of certain Lepidoptera. 397 



band of colour which happened to be at this horizon. 

 There is no evidence that any selection was made, 

 althouoh there is no doubt that the resulting pupse 

 would have been less conspicuous on the black than on 

 the gold. 



We are forced to conclude that the larvte ascended the 

 lessening space, and stopped at the point where the 

 narrow width of the chink would have endangered the 

 success of the process of pupation which is so precarious 

 in this group of Lepidoptera. Such an instinct would 

 be extremely valuable to species pupating in cracks and 

 chinks of stone or bark, and it certainly seems to exist. 

 The evidence of it was equally clear in V. io, and was 

 found in both kinds of case employed with this species 

 (see the level of the bosses of silk on the black part of 

 fig. 6 in Plate XV.). 



As to the relative strength of black and gilt when 

 equal in extent, the intermediate position of the pupae 

 indicates a tolerably equal balance, inclining rather to 

 the side of the latter in the number of light (3)s and the 

 (4). When the extent of the areas becomes relatively 

 unequal, the balance of strength is of course upset, 

 giving black by far the greater power under the par- 

 ticular conditions of the experiment as carried out in the 

 lowest row of compartments. 



2. Experiments on the pupa or Vanessa io, 

 1888, 1891, AND 1892. 



In working in 1886 I had experimented upon a very 

 few individuals of this species, and had shown that 

 they are highly susceptible. I was most anxious to 

 investigate the species very fully, for it appeared to be 

 even more suitable for the purposes of this enquiry than 

 Vanessa urtica. Although the number of individuals 

 tested has been smaller than in the latter species, the 

 results are more decisive, and I think we may con- 

 sider that our knowledge of these two Vancssidm is, in 

 this respect, about on a level. 



The first necessity was the construction of a scale of 

 pupal colours in which each marked form is represented 

 by a number. This was made in 1888, and found to 

 work well in subsequent years. The divisions are made, 

 as far as possible, equivalent to those of V. urticce, and, 

 indeed, the division into 5 classes was the one into 

 which a large series of individuals of V. io most naturally 



