ILLISOIS BIOLOGICAL MONOGRAPHS [48 



SUMMARY 



1. This investigation deals with the homology of all the structures of 

 the head-capsule of one or more representatives of one hundred and five 

 of the one hundred and nine families of Coleoptera listed by Leng in his 

 recent catalogue. One hundred and forty-six genera have been studied 

 and figured, nearly all representing different important subgroups. 



2. This serial study has made it possible to identify the same structures 

 in a wide series of forms, and to definitely fix the homology of all the parts 

 of the head-capsule. 



3. Hypothetical types ha\e been constructed, based on the structure 

 of the head-capsule of generalized insects and Coleoptera. These show 

 the Coleoptera to have developed in general a consolidation of sclerites 

 and a heavier chitinization of the head wall, a compacting of the head as a 

 whole, and an approximation of the dorsal and ventral movable parts 

 at the cephalic end. 



4. The epicranial suture has been identified in all but two of the genera 

 studied. It has proved a great aid in determining the limits of neighboring 

 parts. What may appear to be a distinct epicranial suture may not even 

 be a suture. It is sometimes distinctly invaginated. Its identity can 

 only be definitely fixed by determining the location of the pretentorinae, 

 which are always associated with it. 



5. The limits of the vertex are dependent upon the position of the 

 epicranial suture. In the Rhynchophora nearly all of the snout belongs 

 to the vertex. 



6. The unmodified occipital suture has been identified only in the 

 Adephaga. The cephalic end on the ventral surface is always represented 

 by part of a curving ridge, which is present in all but a few genera. 



7. The supratentorinae have been identified in a few genera, nearly 

 all of which belong to the Staphylinoidea. 



8. The pretentorinae are the great landmarks of the head-capsule 

 and have been identified in all but two genera. They are, in the vast 

 majority of genera, located near the cephalic end of the epicranial arms. 

 A definite determination of the pretentorinae cannot always be made with- 

 out an ental examination of the head. 



9. The size and form of the front is dependent upon the position of the 

 epicranial arms. In the Cerambycoidea it is large. In many genera, 

 as illustrated by Omophron, Harpalus, and Tachinus, it is partly or wholly 

 invaginated. It may probably be rudimentary or wholly lost in many 

 genera in which the mesal parts of the epicranial arms have disappeared. 



