486 GEOGRAPHICAL DISTRIBUTION OF INSECTS. 
under certain limitations, supplies a useful and certain 
criterion. For though none of these plants are wniver- 
sal in isothermal parallels of latitude; yet, as plants are 
more conspicuous than insects, the Entomologist, fur- 
nished with an index of this kind, may by it be di- 
rected in his researches for them; and in all countries 
in which there is a material change of the climate, as 
in France, there will be a proportional change in the 
vegetable accompanied by one in the znsect produc- 
tions. 
ii. In considering the range of insects I shall first ad- 
vert to that of individual species. At the extreme limits 
of phanerogamous vegetation we find a species of hum- 
ble-bee (Bombus arcticus K.), which, though it is not 
known to leave the Arctic circle, has a very extensive 
range to the westward of the meridian of Greenwich, 
having been traced from Greenland to Melville Island ; 
while to the eastward of that meridian it has not been 
met with. In Lapland its place appears to be occupied 
by B. alpinus and lapponicus, with the former of which, 
though quite distinct, it was confounded by O. Fabri- 
cius; but whether these range further eastward of that 
meridian has not been ascertained. From its being 
found in the Lapland Alps*, it may be conjectured that 
B. alpinus ranges as high on this side as B. arcticus on the 
other, and may perhaps be found in Nova Zembla. Some 
species that have been taken in Arctic regions are not 
confined to them. Of this kind is Dytiscus marginalis, 
which appears common in Greenland, abundant in Bri- 
tain, and is dispersed over all Europe; while D. latis- 
* See above, p. 484. 
