174 THE SCOLYTID BEETLES. 



from a club with one or more septa to an anniilated club with chiti- 

 nized sutures and without septa, to a solid club without annulations 

 or septa, or to a conical club with chitinized joints. 



The septum is evidentl}^ the remnant of the chitinized elements 

 of a movable joint, indicating that the progressive modification of 

 the antennae toward the opposite extreme has been by the process 

 of reduction or fusion of two or more joints, while the modification 

 of the funicle has evidently been along the line of accession by divi- 

 sion as is indicated in the funicle of the retrograde sexual forms 

 (fig. 97) and in the nymphs of certain Hemiptera and Isoptera. 



Thus we have in a single organ evidence of progressive modifica- 

 tion by reversed processes which is not unreasonable and does not 

 necessarily conflict with the facts and prmciples of other evolu- 

 tionary processes. 



ANTENNAL SCAPE. 



The antennal scape is variously modified from simple and slender 

 to short, stout, dilated, and fringed, but is of less importance as the 

 bearer of generic characters than either the funicle or the club. 



The Eyes. 



The eyes are variously modified and range from simple, elHptical, 

 round or oval, to emarginate or completely divided and from widely 

 separated on t,he dorsal or ventral area to approximate on one or 

 on both areas. In 114 genera the eyes in 65 are simple, in 98 emargi- 

 nate, and in 10 divided. Among those with simple eyes, 4 have them 

 approximate on the dorsal or ventral areas. 



The Mouthparts. 



The characters of the mouthparts have been quite extensively 

 used by systematists in the definition of genera, but while the writer 

 recognizes that some excellent characters are to be found in the 

 mouthparts, he is convinced that they are by no means essential for 

 the definition or classification of the genera. The principal objection 

 to their use, as every systematist has doubtless recognized, is that 

 they are not available for interpretation without mutilating the spec- 

 imen, which in the case of rare or unique specimens and those 

 from other collections is out of the question. Another serious objec- 

 tion is in the fact that no two balsam mounts of a maxilla of the same 

 species present the same contours and angles, and, therefore, these 

 may appear to be quite different except, perhaps, in the number and 

 relative lengths of the joints of the palpus. 



