104 Geographical Distribution of Insecta. 



served to l)e, for the most part, more warmly coloured than 

 any other kinds. 



Influence of Soil. — As insects do not derive their nourish- 

 ment immediately from the soil, the latter, considered minera- 

 logically, can act on them only indirectly through the me- 

 dium of the plants which grow in it. If there be insects, not 

 of a fossorial kind, which are found only in calcareous soils 

 (according to LatreUle, Licinus, JRhodocera, Cleopatra, and 

 many Dasytes are so circumstanced), it is because the plants 

 on which they feed grow only in such earths. Consequently, 

 an acquaintance with the vegetation of a locality, enables us, 

 in a considerable degree, to determine what kind of insects 

 inhabit it, even although we be ignorant of the kind of nourish- 

 ment they requu-e. 



It is at the same time true, that it is possible, merely from 

 an inspection of the soil of certain countries, to indicate a 

 priori what families of insects are likely to prevail there. 

 Thus, an arid, I'ocky, and above all, a saline soil, such as is 

 found in Central Asia, Peru, and Tucuman, announces, an- 

 teriorly to all examination, the presence of Melasomas. But it 

 is proper to remark, that in this case, in oiu* supposed igno- 

 rance of the vegetation, it is the more imperatively necessary 

 to take note of the temperature, for, in northern countries, 

 tracts are to be found analogous to those of which we now 

 speak, which do not produce a single melasoma. 

 f.' With regard to fossorial species which excavate the soil in 

 order to obtain a place of retreat, and for the purpose of de- 

 positing their eggs, it is obvious that they Mall frequent only 

 such as docs not offer a gi'eat degree of resistance. Each of 

 them, however, shewsmarked preferences ; Sphex, for example, 

 burrows only in fine and very light sand ; Cicindela hyhrida 

 prefers gravel mingled with a little vegetable mould ; Ammo- 

 batiis the beaten earth of pathways, &c. 



Under these two points of view, soil has influence on sta- 

 tions rather th?n habitats, but the inverse takes place with 

 respect to its physical constitution, that is to say, its elevation 

 above the level of the sea, its inequalites, the water on its 

 sm'face, &c. 



As mountains modify the isothermal lines in the same 



