INTRODUCTION. XXU1 



varieties. In this entirely empirical labor, any process, even 

 expedients are allowable. 



Nevertheless, when one gets to the groups, in which the species 

 lie close together, one is often puzzled, and there remains no way 

 of exclusion. 



Once the females determined, proceed to an analogous sorting- 

 out and grouping of the males by species. Attribute to each 

 female species its respective male, beginning by the more easy 

 and proceeding always by way of exclusion. This is a tentative 

 work, in which one succeeds satisfactorily only when familiarized 

 with a group which is being studied. 



As to separating at the outset the Monobia from the Odynerus, 

 the Symmorphus from the Ancisirocerus, the Odynerus from the 

 Epipona, that cannot be done without being well acquainted with 

 these groups so as to place therein at once the insects according 

 to their facies. If one is not far enough advanced to do so, this 

 separation will result quite naturally from the work of determi- 

 nation ; nevertheless, to distinguish the Monobia, it will be neces- 

 sary to dissect the mouth. 



With that operation, we may finish, because we shall have no 

 more to seek but among a small residue of species, whereas had 

 we begun by establishing that distinction, we should have been 

 obliged to dissect the mouths of all the Odynerus which have been 

 excluded from this operation by the mere fact of their determina- 

 tion. A work of determination made according to this manner 

 of proceeding will afford synoptical views that alone will permit 

 one to appreciate the true relations of species. Better than any 

 other, it will prepare the entomologist to give comparative 

 descriptions taken from a general point of view which will not 

 lose itself in worthless details. 



