I02 The Scottish Natiiralist. 



saxifrages, on the Perthshire and Aberdeenshire mountains, de- 

 scending as low as looo feet. It also occurs on the Alps. 



An examination of the distribution given above in detail will 

 show that all the species occur in Scotland ; one (Erebia Epi- 

 phro?i)m Scotland, England, and Ireland; and one {Crambus 

 furcatellus) in Scotland, England, and Wales ; and regarding their 

 exotic distribution, eight species are found in North Europe (seven, 

 if not all, reaching the arctic circle) ; seven are both arctic and 

 alpine ; three are alpine, but not arctic ; and three occur on the 

 Pyrenees (two of these being also arctic); two are found in Ame- 

 rica ; and of four the distribution is imperfectly known. 



The distribution may be presented in tabular form, thus : — 



{ Scotland, .... all. 



British distribution -l Scotland, England, and Ireland, . i 



( Scotland, England, and Wales, . i 



Exotic distribution 



/ Arctic and alpine, . . . 7 



J Arctic or northern only, . . i 



Alpine but not northern, . . 3 



mperfectly ascertained, . . 4 



We are now in a position to inquire. Whence, when, and how 

 did these insects come to Britain ? for I do not suppose that any 

 one entertains the opinion that they (or at least the majority of 

 them) originated in this country. Some conspicuous Lepidoptera 

 are nearly or quite restricted to Britain, and have possibly been 

 evolved from other and alHed species within or near our borders; 

 but the species under consideration, which seem to be confined to 

 this country, probably only appear to be so, because, from their 

 small size and close relationship to other species, they have as 

 yet been overlooked elsewhere. 



Whence, therefore, or from what direction, did tliese mountain 

 Lepidoptera come ? 



When or at what period, relatively to the great mass of the 

 native Lepidoptera? 



How or by what agency and route were they brought in ? 



These are all questions easier to ask than to answer, and may 

 be best considered together. To them we will add still another, 

 What causes have governed and restricted the distribution? 



Britain, as every one is aware, did not — apart from the changes 

 wrought by man's agency — always present the same physical fea- 

 tures that it does at the present day. There was once a time, 



