IIELANOCHEOISM OCCURRING IN CERTAIN SCOTCH SPECIMENS, ETC. 35 



nervures fuscous, a black fimbria, narrow at the anal angle, curved 

 above and reaching the centre, where it forms a crescent, the extreme 

 edge indented and not touching the margin, etc." It may now be 

 well asked how many of the beautiful aberrations sent to us from 

 Scotland under the name cnrtisii really belong to this aberration. 

 Mr. Curtis' type specimen was taken (di tlir Iwath at the back of 

 Mr. Kean's house, in the Isle of Bute, on the 27th of -Tuly, 1825. 



Throughout the wide geographical range of T. orhona, i.e., over the 

 whole of Europe to 59" N. lat.. Western Asia, and Northern Africa, 

 the insect is very little subject to striking variation. An increasing 

 development of the transverse lines in the specimens from the Scilly 

 Isles and certain Mediterranean localities being the most striking 

 feature. It is only in the extreme north-west of its area, i.e., the 

 west, north-west and north of the British Islands, that the variation 

 becomes marked, red replacing the ordinary grey and ochreous-grey 

 on the western shores of Ireland ; whilst in certain restricted parts of 

 Scotland it assumes deep mahogany-brown, black and crimson 

 colorations, which are never seen elsewhere. 



Now, a very pretty theory might be formed (as, indeed, has 

 already been done by Mr. Adkin), that this change is due to cold, 

 since the tendency to dark variation is only found in the more 

 northern portions of our Islands ; but, unfortunately for the theory, 

 (1) the districts in which such melanism is found are exceedingly 

 warm and mild ; '■'(2) the aberrations are not found in the same lati- 

 tudes on the Contment, where tne mean temperature is much lower, 

 and the atmosphere drier than in Scotland. 



Now, whatever may be the cause acting within the organism to 

 give rise to the necessary variations presenting themselves, there can 

 be no doubt that the useful variations presented are seized upon by 

 natural selection, and the directive external force is, in this case, 

 undoubtedly due to the actual environment of the species. The 

 peculiar variations present themselves for selection ; the habit of the 

 dark specimens is to rest on the heaths, peat, etc., in the localities in 

 which they occur ; the variations tending to darken the ground-colour are 

 those most useful to the species ; selection (guided by utility) at once 

 seizes these dark variations, and the melanic forms are the result. 



We are often led to regret that our professional collectors give us 

 so little of their actual field experience to help us in our attempts to 

 explain the phenomena connected with our favourite study. At a 

 meeting of the South London Entomological Society, on April 23rd, 

 Mr. McArthur, whose experience with dark forms of this species is 

 almost unequalled, stated that he considered the dark coloration of the 

 melanic forms of T. orhona to be entirely protective. In the places it 

 haunted — heaths and peat-bogs — it had an entirelydifferent habit from 

 that which it was assumed to have in our southern counties ('•/:., 

 resting under leaves, etc.), for it rested on the ground, and could not 

 hide beneath green leaves, where the latter were not forthcoming for it 

 to hide beneath. The dark form of the insect was to be found resting 

 by day upon the black peat, and it was quite possible for the insect to 



* " Rannoch and Forres can scarcely be compared ; the former is a high' 

 lying, cold, inland district ; the other, lowlying, warm (Forres is one of the 

 mildest and driest places in Scotland) and maritime " (F. B. White, E.M.M., vi., 

 p. 190). 



