GEOGRAPHICAL DISTKIBUTION. 71 



of an insect may be in this way greatly prolonged. Most in- 

 sects live one year. Hatching from the egg in early summer, 

 they pass through the larva state, and in the autumn become 

 pupae, to appear as imagos for a few daj^s or weeks in the 

 succeeding summer. Many Lepidoptera are double-brooded, and 

 some have even three broods, while the parasitic insects such as 

 Lice and Fleas, and many Flies, keep up a constant succession 

 of broods. Warmth, Mr. R. C. R. Jordan remarks in the Ento- 

 mologists' Monthly Magazine, has much to do with rapidity 

 of development, as insects may be forced artificially into hav- 

 ing a second brood during the same season. Some Coleoptera, 

 such as the Lamellicorns, are supposed to live three years in 

 the larva state, the whole time of life being fom- years. The 

 Cockchafer (Melolontha) of Europe is three years in arriving 

 at the perfect state, and the habits of the Goldsmith Beetle 

 (Cotalpa lanigera), according to Rev. Samuel Lockwood 

 (American Naturalist, vol. 2, p. 186), and of the June Beetle, 

 and allied genera, are probably the same. 



Geographical Distribution. The insect-fauna of a coun- 

 try comprises all the insects found within its limits. The 

 Polar, Temperate, and Tropical zones each have their distinct, 

 insect-fauna, and each continent is inhabited by a distinct 

 assemblage of insects. It is also a curious fact that the insect- 

 fauna of the east coast of America resembles, or has many an- 

 alogues in, that of the Eastern hemisphere, and the west coast 

 of one repeats the characteristics of the west coast of the 

 other. Thus some California insects are either the same spe- 

 cies or analogues {i.e. representative species) of European 

 ones, and the Atlantic coast affords forms of which the ana- 

 logues are found in Eastern Asia and in India. This is corre- 

 lated with the climatic features which are repeated on alternate 

 sides of the two hemispheres. 



The limits of these faunae are determined by temperature and 

 natural boundaries, i. e. the ocean and mountain ranges. Thus 

 the insect-fauna of the polar regions is much the same in 

 Europe, Asia, and North America ; certain widely spread polar 

 species being common to all three of these continents. 



When we ascend high mountains situated in the temperate 



