1871.] 45 
ON THE ORIGIN OF BRITISH LEPIDOPTERA. 
BY BR. C. R. JORDAN, M.D. 
The British Isles were, without doubt, peopled with insects by 
migration from the continent ; could we have the how, when, and where, 
of this exodus laid bare before us it would be of intense interest, and it 
may be, therefore, of some use to see what the British Lepidoplera 
teach us upon this subject. 
It has seemed to me that they may be arranged under the following 
heads :— 
Migrants of the glacial epoch. 
Migrants of a warmer post-glacial epoch. 
. Direct migrants. 
. Western migrants. 
Autochthones. 
Oa woh eS 
. Naturalized species. 
These may be discussed in the order here set down: 
1. Migrants of the glacial epoch. 
At a comparatively recent geologic period, England was a country 
of frost and ice, not differing much from what Greenland now is; plants 
flourished in our land before this, and probably, therefore, insects also ; 
of these we have no known record that can be traced; they were de- 
stroyed by the age of ice which followed; but this very period of death 
has yet left an indelible stamp on both the flowers and insects of our 
land; to it we owe the saxifrages and other Alpine plants of our north- 
ern mountains, and to it with equal certainty we owe such insects 
as EHrebia Epiphron and E. Medea, Pachnobia alpina, Dasydia ob- 
Juscaria, Psodos trepidaria, and probably other more exceptional in- 
stances, such as Canonympha Davus, Larentia cesiata, L. flavicinctata, 
&e. If we take Hrebia Epiphron (Cassiope) as an illustration, it is self- 
evident that it could not have reached Sca-fell from the Alps, or the 
Pyrenees, during existing circumstances. It is not found in the Scan- 
dinavian peninsula, so that we cannot suppose it to have come from 
thence ; it is clear, therefore, that there must have been a very different 
condition, both of England and the continent, from the present, in the 
days when it migrated to this distant spot. The only probable time of its 
coming could be during this reign of ice, and it still remains as much a 
witness to the truth of this period as the glacier furrows left on the 
rocks themselves. A careful summary of the geographical distribution 
of our Alpine and sub-Alpine insects, both at home and on the conti- 
nent, would give us juster ideas as to what species may with certainty 
