188 THE SCOLYTID BEETLES. 



(bl ) or the seminal rod (b2), or both, as the case may be. The end plates 

 (&) are commonly present. They are sometimes fused with a£ but 

 are more often separated or more directly connected with hi or 6^.« 

 The end plates proper appear to function as accessories to a in forming 

 the sheath or outer tube; hi ma}^ function as a valve to close the 

 seminal duct while muscular or blood pressure is brought to bear on 

 the ejaculatory sack to force the seminal fluid into the copulatory 

 pouch, or they may function, as indicated by Lindemann, as a furrow 

 or troughlike support for the posterior end of the seminal duct. The 

 end plates are subject to great modification, from simple chitinous 

 pieces, as in Pissodes, to the more complex structure with many parts, 

 as in Dendroctonus (fig. 107), and especially Hylesinus, or into a long 

 slender troughlike rod, as in Ij^s (fig. 103), a stouter rod with apical 

 dilation and a long flagellum, as in Xylehorus, or a brushlike form, as 

 in Micracis (fig. 106), and Xylocleptes. The function of the slender 

 rod or apical filament is not known, but it may serve to conduct the 

 seminal fluid directly into the spermathecal duct. 



When we consider the enormous range of possibilities in the modifi- 

 cation of tergal and plem'al sclerites, as manifested in the tergum and 

 pleura of the metathoracic segment, we can readily understand that 

 the most complicated and complex copulatory apparatus yet found 

 in insects is comparatively simple and that the possibilities of further 

 modification have not been exhausted. 



The tegmen, or ring (c), is. generally present but may be obscure or 

 absent. There is a wide range of variation, from a simple and ven- 

 tral plate {Scolytus ruguhsus, fig. 108) or fork (S. quadrisjnnosus, 

 fig. 109, and Crossotarsus , fig. 110) to a continuous simple ring or band 

 (fig. 102), and from a plain or forked dorsal piece to a forked or plain 

 ventral piece. In nearly all cases it functions as an apodeme for the 

 attachment of the primary and accessory muscles for the posterior 

 extension and movements of elements a and h. The sections of the 

 various forms of the tegmen may be referred to as (cl ) the posterior 

 section, (c^) the median section, and (c3) the apodemal process. 

 Section cl may be either dorsal or ventral; in whichever case section 

 c2 will occupy the opposite position. 



The spicule or rod (element d) is usually present in a more or less 

 distinct form which may vary from a curved forked rod to a simple 

 rod, and in its various modifications and functions may occupy a 

 dorsal, sublateral, lateral, or subventral position. The sections of 

 the various forms may be referred to as the anterior section (dl) and 

 the posterior section (d2). It functions as an apodeme for the attach- 



« Verhoeff (1896) and Niisslin (1912) considered tlie end plates as belonging to the 

 body. 



