MELANOCHROISM IN BRITISH LEPIDOPTERA. 221 



venture to give my own experience of melanism as I find it in the 

 field. 



I have spent several months during each of the last six summers 

 in collecting on and around that great mass of peat and granite known 

 as Dartmoor. There in the midst of hills, intersected by densely 

 wooded and well watered valleys, with a great rainfall and little sun- 

 shine, we have, seemingly, every essential condition for the production 

 of melanic forms. 



Now, take the two great natural divisions, the hills running up to 

 2000 feet, and the wooded valleys between them. In the second 

 of these divisions — the wooded valleys — although some species are 

 found that show no signs of variation, others, such as the Satyridce, 

 show very great divergence from the tyj^e, for instance, Pararge 

 cetjeria in the open country is of the ordinary type-form, but directly 

 you descend to the valleys the specimens become visibly darker, and 

 tlie darkest I took was beaten out of an alder-swamp where no sun 

 could penetrate. The same may be said of P. megcera. Other species 

 seem to develop spots and rings such as Epiniphele tithonus and 

 E. hyperanthus. This tendency to variation occurring in one family, 

 but not extending to all, inclines me to support the idea " that wet 

 and dark places act only upon a species having a latent tendency to 

 melanism." Then again the specimens from low- lying situations of 

 Polyommatus pMceas are darker than those from the open moor, indeed, 

 I have taken this year (in spite of the great drought) almost black 

 specimens, with no red showing at all on the hind wings. Two moths 

 (which I may call ground-resting insects) are always dark on the 

 moor itself, viz., Gnophos obscnrarta and Aeidalia viarginepunctata, 

 while Tephrosia biunrhdaria, an insect taken on trunks of trees, in the 

 darkest situations does not show any tendency towards melanism. 

 Many other instances might be mentioned among other families, 

 and my experience is that while the ordinary tyi^e-form of any insect 

 may be taken in dark hollows, the melanic form is never found in the 

 open sunshine. Therefore, absence of light would seem to be a more 

 powerful factor in their jjroduction than dampness, though, in order 

 to produce them, both conditions must be combined. — John N. Still, 

 Bridestowe, Devon. 



It appears to be an undoubted fact that some animals have the 

 immediate power of assimilating their colour to their surroundings, but 

 those on which experiments have been made to test this result are much 

 higher in the scale than Insecta ; all I believe are Vertebrata, and I do not 

 think any of our insects can respond to their environment in this way, 

 and I am most certainly convinced that when a leijidopterous insect 

 emerges from pupa, its colours are fixed and final. Of course there is 

 sometimes a change due to loss of scales, and even the collector, pure 

 and simple, is awake to this fact if you try to exchange them with him. 

 I do not know that Major Still supposes such a thing possible in 

 lepidoptera, and therefore the above must be simply taken as my own 

 personal disbelief in such a possibility in insects. 



I am not at all clear yet as to how Ave can determine which insects 

 have, and which have not "a latent tendency to melanism," although 

 Major Still's suggestion is on the right road. If in a district where 

 melanism is prevalent, certain species persistently refuse to be melanic, 

 there is a strong 2)rima facie reason for supposing that such species have 



