14 EEPOET OF THE SECEETAEY. 



The knowledge of the American fauna is not yet advanced enough to 

 allow us to draw with certainty an inference as to the affinities of the 

 species between them so as to prejudge their filiation. However, I 

 have made more than one remark on this topic, and I will hazard a few 

 words on the matter when speaking of genera and species. But I re- 

 serve for another work the statement of comparisons which seem to me 

 to cast some light on the dispersion of the vespidoe on the surface of tile 

 globe and on the modifications which have been worked off under 

 diverse latitudes; in other terms, on the origin of actual existing faunae. 



"The complex affinities of species, and still more the filiations which 

 arise from these affinities, become obvious to the eye only when one 

 has acquired a perfect knowledge of the species and genera of a fauna. 

 To seize them in all their extent, it is necessary to know, as it were, all 

 the species of the group by heart in order to be able to take it in at a 

 glance, or to examine at pleasure each part in the picture that one has 

 formed in one's memory. Only when one has attained this point in the 

 study of the group is it possible from the inspection of a species to feel 

 its affinities, for they do not always appear in the more easily appreci- 

 able characteristics. They often discover themselves in certain charac- 

 teristics of appearance which are, at times, of great importance, but 

 which are not seized at a glance, or in certain relationships of form, 

 which a long practice teaches one to distinguish easily, though they can 

 scarcely be defined. 



"The first basis of philosophical zoology is the profound knowledge 

 of the detail of faunae. To give an idea as complete as possible of the 

 faunae of the vespidje of America is the jrarpose of this volume. 



" The plan which I have decided on, in drawing up this work, is the 

 following : 



" I give as far as possible the complete description of the species 

 which belong to the fauna of North America, considering as such all 

 those which i>eople the new continent to the north of the Isthmus of 

 Panama, including likewise the Antilles. This work is, therefore, more 

 especially a monograph of the vespidae of the United States, of Mexico, 

 and of the Antilles. Besides, I have added, as a complement, the cata- 

 logue of all the species known till now in the rest of America, and I 

 have found it a great advantage for the classification, the method becom- 

 ing thus more complete. Moreover, this plan allows me to enunciate 

 views on the geography of insects, on the dispersion of the species, and 

 on the modifications which take place under the influence of diverse 

 latitudes. 



'• I have confined myself, for the species of South America, to making 

 a catalogue of them, not having materials sufficient for a monograph. 

 For those, however, of which I had the types under my eyes, I have 

 given Latin diagnoses, in order to present them in a comparative 

 manner wi th respect to the surrounding species and also to complete 



