Xll INTRODUCTION. 



forms combined with that of their geographical distribution, comes 

 afterwards to throw light on the cause of the filiation which the 

 graduated resemblances of the species serve to reveal to us. It 

 shows that this filiation obeys laws which have also their regu- 

 larity, in so far as they are intimately counected with the physical 

 laws which hold sway in every region of our globe. 



Toward these grand philosophical queries, zoology ought 

 iu our time to tend, and species should be studied with a view 

 to the solution of such questions. As in geology, the study of 

 the actual existing state of the earth's crust, and the appreciation 

 of the phenomena that there take place, of the intimate trans- 

 formation of rocks, of the mechanical disturbance of the layers, 

 of their reconstruction under new forms, allows us to draw an 

 inference by analogy as to the more ancient transformations, and 

 the agents which have produced them; so the study of species, 

 and of their actual existing transformations seems likely to enable 

 us to follow up the chain of these transformations to a point more 

 or less close to their origin. 



The definition of the first divergences observable in the perma- 

 nent varieties which may be considered as nascent species, in 

 order to ascend afterwards to the relationship of species separated 

 by divergences more and more profound, such is, we deem, the 

 point of view under which we should never neglect to study 

 species. 



Zoology, only when considered from this point of view is 

 philosophical. It has not its aim in itself; it serves only as a 

 means to sift questions of a higher order. Now entomology is 

 precisely the one of the branches of zoology, in which the study 

 of the filiation of species may become the most fruitful in results, 

 either on account of the multitude of ramifications of general 

 types and of the multiplicity of forms under which each type 

 appears, or on account of the smallness of the breaks which sepa- 

 rate genera and species, or also on account of the immense variety 

 of forms and of the facility with which species seem to become 

 modified in proportion as they spread over the surface of the 

 globe in diverging ways. Thanks to all these causes, it is not 

 difficult to find examples of every kind of filiation, not difficult 

 either to follow over latitudes certain still recent modifications 

 which allow us to draw an inference by analogy as to other 



