Geographical Distribution of Insects. 97 



regard to the physical natui'e of the localities in which they 

 are found. Thus, some live in water or on land ; some on 

 leaves, others in carcasses — this constitutes then- station. 2d, 

 in relation to their geographical position, that is the country 

 to which they are indigenous ; and this is what is called their 

 habitation, or, by abbreviation, their habitat. Under these 

 two points of view, genera, tribes, families, and any other 

 kind of group, can be equally well considered as individual 

 species. 



In regard to both of them, the entomologist has the two 

 following questions to propose to himself, and it is not till he 

 is in a condition to reply to them that the science can be con- 

 sidered as complete. 



1st, A locality or a coimtry being given, what are the spe- 

 cies of insects which are foimd there ? 



2d, A species or a group being given, what is the country 

 or locality which it inhabits ? 



Previously, however, to entering upon the examination of 

 stations and habitats, an important problem presents itself, 

 namely, why species inhabit such and such a locality, rather 

 than others .'' The only means by which it can be solved is 

 to ascertain how far external physical circumstances act upon 

 species ; and, if these are insufficient to explain the mat- 

 ter, we must revert to a higher cause — that, namely, 

 which ordained the order of things as they now actually 

 exist. 



Influence of External Circumstances on Insects. — It is not in 

 our power to explain why the organization of living beings is, 

 in certain cases, acted upon by physical agents, and in other 

 cases exempted from this influence ; but the fact of such a 

 difference existing is proved by observation, and it is the fact 

 alone which is of importance in the present inquiry. 



External circumstances do not act on animals and vege- 

 tables, either in the same degree or in the same order. Ve- 

 getables are fixed to the soil, and, deriving their nourishment 

 immediately from it and from the atmosphere, are placed in 

 most intimate relation with the earth, air, light, water, &c. 

 while animals having the power of motion, can, at pleasure, 

 witlidraw themselves to a certain point from the action of 



VOL. XXVII. NO. hill. JULY 183^'. o 



