xv [ INTRODUCTION. 



■ color only a sec Miliary importance, on account of its fre- 



. However, there is nothing absolutely fixed 



in nature; the forms and the sculpture likewise vary within 



in limits. Therefore the descriptions can he only averages 



deduced from a certain number of individuals. The description 



dd represent, as it were, the algebraical formula of the 



species, or its ideal type. It is not required that this should tally 



with the individual, hut, on the contrary, that it should represent 



f the characteristics of the ensemble of individuals. 



in practice, the description can never be so perfect, since it 



is drawn from a certain number of individuals and not from the 



idividuals that represent the species. It is for 



the reader to know how to seize the connection that exists between 



the description and the heterogeneous individuals which he 



may have beneath his eyes. In a word, my method of description 



aims above all at generalizing, and requires that the reader should 



ralize likewise. It can hardly suit the amateur inclined to 



himself in a multiplicity of details, for whom the collection 



takes the place of nature, ami for whom the determination of an 



individual i- the final purpose of the study of a species. 



From the principles jusl laid down, it follows that in the extreme 

 subdivisions of genera, I have usually preferred the characteristics 

 taken from the form to those taken from the color. Undoubtedly 

 it eenient for the reader, for the natural method is 



always less easy to follow than the empirical systems; never- 

 theless, 1 think that it is preferable to proceed in that wise, for 

 whatever may lie done to seek the natural method, a large portion 

 i is sure to remain, as I shall endeavor to show in 

 study concerning the filiation of the species. AVe cannot, 

 therefore, abstain too carefully from classification of empirical 

 nts. l 



1 It i< necessary t - observe en this head that no absolute rule can be 

 laid down as to the subordination of characteristics. To lie sure, forms 

 varying less than colors, they offer, in general, characteristics more im- 

 portant than the latter; hut there is, however, now and then a case in 

 which the colors are more fixed than certain forms, and assume a real 

 importance— for instanoe, as being the stamp peculiar to a certain geo- 

 graphical lone. Thus, the division Hypodynerns (genus Odynerus), which 



depends greatly en ti lors and fades, and which comprises the most 



divergent forms. In this case, the livery becomes the stamp of a fauna, 



