MILD WINTER. 19 



not in the earth but upon plants, and arc therefore much less 

 protected from the inclemencies of the weather during their 

 development than the insects with a complete metamorphosis. 

 The chief habitation of these insects is therefore between the 

 tropics, in the lands which know no winter, where their deve- 

 lopment can go on uninterruptedly. This applies particularly 

 to the Reduviidse, Scutata, and Coreodea, which are found in 

 astonishing abundance and variety in warm countries. Only 

 a comparatively small number of these insects can .exist in 

 countries where their development is interrupted by a long cold 

 winter. 



Insects with a complete metamorphosis, on the other hand, 

 pass the winter in the egg, larva, or pupa state, dormant in the 

 interior of plants or deep down in the earth, and are thus almost 

 entirely out of reach of the action of cold. Thus the cold of 

 winter has little influence upon them ; but the summer tempe- 

 rature has a great effect. A country with a cold winter and a 

 hot summer has therefore more southern insects with a com- 

 plete metamorphosis than a region of similar mean annual 

 temperature more uniformly distributed, because in the case of 

 insects with a complete metamorphosis, as in that of annual 

 plants, the summer temperature is really the sole considera- 

 tion of importance; while for perennial and especially woody 

 plants, and for many insects with an incomplete metamorphosis, 

 the winter temperature is also of great consequence. This 

 explains why, in America, tropical forms of insects and cul- 

 tivated annual plants (such as maize), but not tropical forms 

 of trees, advance further towards the north than in Europe, 

 because under the same latitudes (at least on the east side of 

 the American continent) the summer is hotter and the winter 

 much colder than in Europe. And inversely, from the circum- 

 stance that in (Eningen the insects with incomplete metamor- 

 phosis exhibit more tropical forms than those in which the 

 metamorphosis is complete, we may infer that in CEningian 

 times the winters must have been very mild, the temperature of 

 the winter rather than of the summer having been higher in 

 the Swiss Miocene country than that now prevailing in Central 

 Europe. 



Insects in general, being of a small size, do not attract much 



c2 



