57 
males with a white ground colour occasionally occur in the south, but 
they are always large and therefore different in appearance from 
northern specimens. Big dull-brown females also occur as a rare 
aberration, in southern woods. Again, even in the extreme north, 
cream-coloured males are found occasionally, but they have a dingy- 
greyish appearance, and are of small size. In the midlands, where the 
races overlap, a mingling of characters as regards size and colour takes 
place. 
The difference in size is very considerable; my Scottish males 
range from 24mm.-32mm. in expanse, my Irish from 36mm.-38mm., and 
my English from 36mm.-40mm. It is, however, not unusual to find a 
reduction in the size of an insect as one proceeds northwards, but the 
difference in colour is more important. It cannot be explained on the 
ground of different surroundings, for the insect always lives in pine 
woods, and indeed the colouring of the upperside is not cryptic at all — 
for only the underside is visible when the insect is at rest—and we 
must seek for some other explanation. 
In Scandinavia Lampor states that in the male the wings are 
black and white, but that ab. flaveacens, Buch-White, is found in 
Sweden (Ostergolland, Sodermanland, Upland) and in Norway, south 
and centre, but the type is the prevalent form in Sweden, Norway 
south and middle, Finland and Denmark; Aurivillius (Macrolep. of 
Sweden, Norway, Denmark and Finland), says in the male the upper- 
side is black and white, seldom yellow (ab. flavescens, Buch-White) and 
and in the female ochreous with two dark cross lines and a white dark 
apical mark, but sometimes more like the male, and then greyish in 
the centre instead of yellow ochre. 
In these islands the small white form occurs in Scotland, N. 
England, extending into the midlands, in Wales, and over the whole 
of Ireland, and this is the area commonly occupied by that part of our 
fauna derived from Scandinavia. It seems curious that the whole of 
Ireland should be occupied by Scandinavian forms accustomed to a 
very different climate, hut that it is the case must strike the least 
•observant. 
In the case of mammals the best instance is the blue or mountain 
hare, Lepns timidus, which is found in North Scotland, but not 
elsewhere in Great Britain, being replaced in the south by the brown 
hare, L. europaeus, but occurs all over Ireland, where the brown species 
is unknown. 
In lepidoptera a few instances having the same distribution will 
■suffice: Coenonympha typlion, Trochilium scoliaefonne, Acronycta myricac, 
Hadena rectilinea, Larentia salicata , all of which are found even in the 
■extreme south of Ireland. 
The probable explanation is that they reached this country when 
Scotland was joined to Scandinavia, and Ireland to Scotland. The 
rough map I hand round will show the supposed former land 
connections, and are derived from Scharff’s “ European Mammals.” 
A large river rose in South Scotland and ran to the Atlantic, down 
what is now the centre of the Irish Sea, another large river ran down 
to the Atlantic along the English Channel; Scandinavia, the British 
Isles and France were all united directly. England remained connected 
xxii.-xxiii. 
