48 [July, 1871. 
flexilis, a plant whose most noted continental locality is near Stettin. A 
western migration amongst insects is also rendered probable by the 
distribution of some species, such as Tvrochiliwm philanthiforme and 
Polia nigrocincta; but a careful comparision of the insects of Galicia, 
Brittany, Cornwall, and the Isle of Man, is yet to be made. 
The question is here brought prominently before us as to whether 
there was ever any direct junction between our islands and the conti- 
nent of America. The Lepidoptera of the two localities give us no proof 
of this ; true, there are many insects common to England and America, 
but none that are peculiar to the two. With regard to Chionobas Jutta 
(and if Colias Hecla and Colias Boothii be the same, in its case also), we 
can say this insect must have reached America through Iceland ; but 
this is not the case with any British insect; on the contrary, the 
presence of Vanessa Antiopa,with Pieris Protodice,so closely allied to Pie- 
ris Daplidice, Libythea Bachmanni, and Deilephila Chamenerii, Libythea 
Celtis, and Deilephila galii, seems to point to a place of junction de- 
cidedly to the south of our islands. Such a union would block up all 
passage between the northern and southern portions of the Atlantic, 
and there would be no possible gulf-stream on our western coasts: this 
might be, therefore, the very cause of the glacial period, and it must 
have been co-existent with it,—at all events the union could not have 
been at a later epoch. 
It seems most probable, on a careful examination of the facts, that 
there has been a western migration of insects as well as plants, but that 
further investigation on this point is needed ; we have no right, however, 
to expect to find our western insects in America. The Lepidoptera 
common to the two continents can all be accounted for by a more 
southern junction. This migration was, as said before, probably at or 
before the glacial period; and it is remarkable how little change has 
happened to the insects considering the immense lapse of time and the 
change of climate. The uniform tendency of that change in many cases 
is, however, worthy of note; thus, Vanessa Antiopa, Vanessa cardui, and 
ilelanippe hastata are all darker than in Europe ; this change is more 
marked in Deilephila Chamenerii and D. galii, Phlogophora Iris and 
P. meticulosa, and it becomes still more decided in Vanessa Milberti as 
compared with V. urtice, V. J.-aluum and V. polychloros, Thanaos 
brize and Thanaos Tages. Who, onseeing this, can risk the belief that 
these so-called representative species are in reality climatic varieties P 
Truth compels us to state that this change is not always constant; thus 
Lycena phleas, Deilephila lineata, Scoliopteryx libatrix, and Hucosmia 
wndulata seem to have: undergone no variation from the same species 
