NORTH AMERICAN ACROLOPHIDAE — ^HASBROUCK 511 



The uncus (un, figs. 3-6) is the posterior, dorsal projection of the 

 genitaha above the anal opening. It is heavily sclerotized, normally 

 hooldike, and it may be naked or setose. It may be simple, termina- 

 ting caudad in an uncal process (up, fig. 3), or it may exhibit varying 

 degrees of bifurcation and terminate in a pair of furcae (uf, fig. 4). 

 The form of the uncus is peculiar to certain species and to a few 

 species groups. 



The socii, paired organs lateral to the anal opening, are entirely 

 absent in all acrolophids. 



The gnathos (gn, figs. 3-6), an organ ventral to the anus, arises from 

 an area near the base of the uncus. Its median ventral plate may be 

 considered absent, or at least it is not differentiated as a distinct part. 

 It may be simple, occurring as a fused and well sclerotized structure 

 (fig. 3), or it may exhibit varying degrees of bifurcation into a pair of 

 lateral arms (lagn, fig. 4). As in the case of the uncus, the form of the 

 gnathos is peculiar to certain species and species groups. In some 

 species having the fused gnathos, the apical portion of this organ is 

 clothed ventrad with numerous, minute, seta-like processes which may 

 have a sensory function during copulation. 



The tegumen (tg, figs. 3-6) is actually the remainmg external 

 covering of the ninth and tenth segments which has not been differ- 

 entiated into the foregoing parts and from which these parts originate 

 as specialized sclerite structures. However, the entire sclerotized 

 portion of the tegumen is considered to be a part of the tenth segment 

 (i. e., the tenth tergum), the ninth segment being greatly reduced and 

 contmued dorsad as a membrane only. The sclerotized part of the 

 tegumen articulates at its lower extremities with the vinculum and 

 from it arise the uncus and gnathos. In the present revision, the 

 lateral extensions of the tegumen are called lateral arms (latg, figs. 

 3, 5-6). 



In a number of species, there is no clear line of demarcation sepa- 

 rating the heavily sclerotized aedeagus from the membranous, ever- 

 sible vesica. In such cases, between these two structures there is 

 a transitional area exhibiting a gradual change in degree of scleroti- 

 zation. In some species, such as A.filicicornis, where this area of tran- 

 sition is armed, it may be diflScult to determine whether such armature 

 belongs to the aedeagus (as spines) or to the vesica (as cornuti). When 

 fluid is forced into a genital capsule which has been softened by treat- 

 ment in potassium hydroxide, the vesica is commonly caused to expand 

 and reveal the true origin of such processes. In a few species, how- 

 ever, it has not been possible to ascertain satisfactorily whether these 

 processes are spines or cornuti. In such cases, they are simply con- 

 sidered as armature of the transitional area. 



