On the Geographical Distribution of Insects. 341 



chrysalid form. The reason of this is, that the leaves of pe- 

 rennial plants appear earlier than those of annuals, so that the 

 young caterpillars find them a ready food as soon as hatched, 

 which could not be the case with those living on the other. 



The majority of the species which hybernate as lar^^ae, is ne- 

 cessarily composed of those which live in that state for seve- 

 ral years, such as Melolontha vulgaris, Lucanus cervus, the 

 greater part of the Longicornes, many Elateridae and Bupres- 

 tidae, Ijepidoptera with endophytous larvae, &c. The remain- 

 der consist of larvae disclosed about the middle of autumn, and 

 which have been surprised by the cold before accomplishing 

 their change into a pupa. 



Hybernating pupae belong almost entirely to the lepidopte- 

 rous order, and to the species which, as has been seen, live on 

 annual plants. These chrysalides await disclosure till the 

 Mowers appear on which the butterfly feeds, so that, in gene- 

 ral, they are not earlier than the kinds which passed the winter 

 in the state of egg or larva. 



Finally, a great number of perfect insects hybernate, and 

 shew themselves not only in spring, but even during warm 

 days in winter. The greater part of these are Coleoptera, 

 and chiefly of a carnivorous or Kgnivorous kind, as both these 

 may still find some alimentary substances at that season, 

 although it is probable, considering the almost complete disap- 

 pearance of their fatty tissue in spring, they reqiure but veiy 

 little nourishment in this interval. The principal cause of 

 the hybernation of these species seems to be, that the sexual 

 union has not taken place, the non-accomplishment of the 

 generative functions having the greatest influence on the 

 longevity of insects. 



The order in which the various species appear on the return 

 of spring is thus determined, in a great measure, at the close 

 of the preceding autumn. During the remainder of the warm 

 season it is regulated by the number of generations, and the 

 period which each species requires to undergo its metamor- 

 phosis. These appearances coincide in general with the 

 flowering of certain plants, so that it is possible to divide the 

 year, ;i.s has been done by Kirby and Spence, into different 



