168 THE SCOLYTID BEETLES. 



nant characters. Here, again, there are a number of changeable and 

 frequently parallel characters, the progressive modification of which 

 shows many divergmg lines toward the extreme, as, for example, 

 the greatest development of jointed and differentiated appendages * 

 in the larvae, the large size, the odd shapes, and the extraordinary 

 elements of structure and habit. 



It is evident that the scolytoid beetles could not have been derived 

 from the highly differentiated carabids or scarabseids and that thesa 

 groups could not have been derived from any existing group of the 

 Rhynchophora. It is also evident that the species in the two primary 

 divisions of the Coleoptera which may be the nearest representatives 

 of their primitive ancestors are themselves so highly differentiated 

 from one another and from ancestral forms of Coleoptera that they 

 can not be recognized, or, K they could, they would be of little or no 

 use as a basis for speculation on the origin and evolution of the order; 

 then, too, we have no material m fossils on which to base a reliable 

 hyi^othesis, because only the highly specialized forms ha^'e been pre- 

 served. Therefore we must rely on facts as they exist and endeavor 

 to discover and mterpret the elements of distinction and relationship 

 which have survived in the course of their evolution, under the influ- 

 ence of natural selection, dommant differentiation, and progressive 

 and parallel evolution. The writer's interpretation of these facts, 

 so far as they apply to morphological characters and the distinction 

 of groups and species, will be expressed in the tables of families, sub- 

 families, genera, and species, in the succeedmg contributions toward 

 a monograph; as will also the progressive modification of characters 

 indicative of the lines of divergence from one extreme toward the 

 opposite. 



GENERAL ANATOMY. 



The discussion, illustrations, and terminology of the anatomical 

 elements of Dendroctonus given in Part I of this bulletin wiU serve 

 as a basis for comparing the anatomy of representatives of other 

 genera. The writer has made a detailed study of the entire anatomy 

 of only a few representatives of other genera, but the more important 

 elements of the external and internal anatomy of representatives 

 of aU of the genera in the local collections have been studied, involv- 

 mg the preparation of over 1,200 microscope slides. This, together 

 with the work of other investigators, notably Liademann, Ntisslin, 

 Fuchs, and Eichhoff, gives us a basis for a somewhat comprehensive 

 view of the subject. There remains, however, an immense amount 

 of anatomical work to be done before a knowledge of the subject is 

 anything like complete. 



a The writer holds that it is by no means proven that larvae with jointed append- 

 ages are more primitive than those without such appendages. 



