190 THE SCOLYTID BEETLES. 



tergite, as in Crossotarsus. In Dendroctonus the retractile muscles 

 {e2) are attached to the anterior end of the spicule {d) and to the 

 basal angles of the body (a) , while in Crossotarsus they are attached 

 to e2 and to the sides of a ventral groove in a. 



The connecting membrane (/) is very difficult to locate and follow- 

 to its primary connections, but if it could be accurately traced it 

 would doubtless furnish good evidence as to the proper assignment of 

 the chitinous elements to their respective tergal and sternal origins, 

 unless, as is the case with muscles, the attachments are changed or 

 even reversed to harmonize and economize the requirements of func- 

 tion. The connecting membrane between the posterior section of 

 element d and the eighth abdominal sternite in Dendroctonus seems 

 to furnish quite conclusive evidence that the spicule represents the 

 ninth sternite. 



ANTERIOR AND MEDIAN ELEMENTS. 



The anterior (4) and median elements (3) of the male reproduc- 

 tive organs have received special attention by Niisslin, who bases a 

 classification on the length of the ductus ej aculatorius (Sh) and the 

 character of the testes (4&) , seminal vesicles (3) , vas deferens (4a) and 

 mucous glands (£c) . 



VARIATIONS AND COMBINATIONS OF THE ELEMENTS. 



Various combinations of the elements of the copulatory apparatus 

 are found in the species of allied genera. Quite a wide range of varia- 

 tion is also found in the character of the elements in the species of 

 the same genus. Even species which in all other respects appear to 

 be closely alhed have very different characters, either in the form 

 of one or more elements or in different combinations of the elements. 



In Division I of the family Ipidse the absence of the seminal valve 

 and the presence of the seminal rod appear to predominate. The 

 valve, as a definite part, is absent in 21 genera and 52 species and 

 present in 10 genera and 16 species. The rod is present in 25 genera 

 and 55 species and absent in 8 genera and 14 species. Both the rod 

 and valve appear to be absent in 6 genera and 10 species, representing 

 4 subfamilies, and both are present in 10 genera and 15 species, repre- 

 senting the same four subfamilies, and especially in Corthylinae. The 

 striking feature of the Subfamily Ipinse is the apparent ^ separation 

 of the femora from the body, especially in Ips and the closely allied 

 genera. In PityopJithorus (figs. 104, 105) they are found to be fused 

 with the body in some species and separated in others; within still 

 other species there is a supplementary band (aS) connecting them 

 at or near the base. 



a The writer has found that the femora are connected to the body by ligaments. 



