Of _satyrion_ I have little personal experience. I only twice found it, namely at Zinal, and at Hallstatt in Austria, but it occurs at Zermatt, Arolla, and in several Swiss localities above 5,000 feet, and I understand that it is the typical Alpine form in the Engadine. With its darkened colour and reduced size it might well be expected to be a still further stunted form of _darwiniana_. Yet I have never found the one succeed to the other at the higher levels. If _darwiniana_ appears when Alpine conditions are reached in a valley it will be met with up to the highest level at which such butterflies live. Tutt was of opinion that _satyrion_ is a distinct species.[20] I once, at the top of the Vorderrheinthal caught a sample of _darwiniana_ a few of which (males) were so dark and had the eye spots so poorly developed that they looked like transitions to _satyrion_. Otherwise I never found any such transitional forms and they are certainly exceptional. There is further a record[21] of _satyrion_ having been taken flying with _arcania_. This was near Susa, at about 2,000 feet I infer. Mr. H. E. Page has similar specimens from Caud and from St. Anton (Arlberg). The females, however, both of mine and of Mr. Page's samples are a pale brown, quite unlike the females both of _arcania_ and of the dark Zinal _satyrion_. The difficulty thus raised has not I think yet been considered by the authorities, and it is possible that the Alpine forms of _arcania_ are in reality three, not two. The evidence taken together suggests, I think, that _darwiniana_ is related to _arcania_ much as so many of the Alpine varieties of plants are to the well-developed individuals of the lower levels. I do not anticipate that factorial differences will be found in these insects, and it is by no means impossible that the distinctions between them are the direct consequences of altered conditions. The relations of _arcania_ to _satyrion_ are more doubtful, and in that case a factorial difference may at least be suspected.