THE GENUS DENDROCTONUS. 7 



abundance of material at hand and because of the comparatively 

 large size of the individuals of this species. Sufficient comparative 

 studies have been made, however, of the other species of the genus 

 and of representatives of other genera of the family and suborders to 

 form a reliable basis for the interpretations and conclusions relating 

 to the more important taxonomic characters and the significance of 

 their modifications in the distinction of species, genera, etc. 



Through the assistance of Mr. R. E. Snodgrass an extensive investi- 

 gation has also been made of the thoracic segments of representa- 

 tives of all of the principal orders of insects. The results have 

 served as additional data and evidence on which to base conclusions 

 in this paper, and will be utilized by Mr. Snodgrass as a basis for 

 a more detailed discussion in a paper entitled "The Thorax of Insects 

 and the Articulations of the Wings," to be published later. This 

 will include a quite complete bibliography and references to the 

 principal systems of nomenclature proposed or adopted by the lead- 

 ing authors, thus rendering it unnecessary to include extensive 

 bibliographic references in the present paper. 



In all of this anatomical work the object of the author has been to 

 acquire direct information on the facts as they exist in the subjects ex- 

 amined; such information to furnish a basis for the determination, 

 naming, description, and illustration of the anatomical elements as 

 represented in the scolytid beetles, and at the same time to serve 

 as a guide to the determination of further facts relating to insect 

 anatomy in general. 



The literature on insect anatomy has been utilized as a guide in 

 securing additional information on the facts and principles involved, 

 and with the idea of adopting such interpretations and nomen- 

 clature as appeared to conform more nearly to the facts and con- 

 tribute to uniformity. No attempt- is made to discuss the merits 

 of opposing opinions or theories, or to prove or disprove them. 



In this presentation of the results of independent investigation 

 and discussion of the facts as interpreted by the author, it is hoped 

 that something has been accomplished toward the advancement of 

 information on the general subject of insect anatomy, and that its 

 special reference to the anatomy of the scolytid beetles will make 

 the future systematic study of this troublesome group less difficult 

 and more accurate, and thus lead to the determination of bionomic 

 and economic data of immediate practical importance. 



NOMENCLATURE . 



There is yet much confusion in the literature and considerable 

 difference of opinion among the best authorities in regard to ana- 

 tomical nomenclature as applied to the structure of insects in gen- 

 eral and especially to representatives of different orders. There is 



