4-98 GEOGRAPHICAL DISTRIBUTION OF INSECTS. 



torial genera accompany the date, the sugar-cane, the 

 indigo and banana a . The idea is very ingenious, and, 

 under certain limitations, supplies a useful and certain 

 criterion. For though none of these plants are univer- 

 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 insect 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), 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. Fabricius ; but whe- 

 ther 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, 



* Geographic, &c. 20. b See above, p. 494. 



