1 1 2 Burnside. 



we see the trees, and quite in the distance, the little bridge 

 on which we stood in the early morning. You cannot see 

 the bridge ? Well, never mind, perhaps it is only fancy 

 that makes me believe that I can ; we know it is there 

 though, and that will do as well. 



We keep near the burn, and tap the birch trunks as we 

 pass. From yonder tree flies our Carpet moth again. Most of 

 those we see here are of a whitish colour, with a pale slaty 

 hue, and with a few wavy lines running transversely across 

 the wings. Observe how well their colour harmonises with 

 the pale silvery bark of the birch ! There is a dark one 

 very conspicuous on the trunk of this tree, but we readily 

 understand that as some of the moths rest on the dark 

 rocks as well, Nature protects some dark ones every year, 

 and with two such strongly opposed conditions working side 

 by side, there will be a distinct tendency to produce two 

 different forms. The search by the birds on the birch 

 trunks alone would lead to the extermination of the dark 

 forms and the preservation of the pale ones, whilst on the 

 other hand, the search on the dark rocks must result in the 

 extermination of the pale forms and the preservation of the 

 dark. Hence, either of these conditions by itself would tend 

 to produce a dark race on the dark rocks or a pale race on 

 the birch trunks, whilst by their united action, dark and pale 

 forms are produced side by side, and the variation of this 

 moth is maintained. The predominance of the pale speci- 

 men here shows, however, that the habit of the carpet moth 

 on the banks of this rolling burn is to rest on the birch 

 trunks in preference to the rocks. 



We are still some eight hundred feet above the loch, and 

 now we leave the burn, and climb the sloping side of Tom 



