214 GENITALIA OF MALE DIPTERA AND MECOPTERA 



genital styles, it is preferable to designate the basal and distal 

 segments of these styles simply as the basistylus and dististylus 

 respectively, (until the matter is finally settled) if we are to 

 avoid confusion. The latter designations are descriptive and 

 also indicate the probable nature of the structures in question, 

 so that it has seemed preferable to adopt them in the present 

 discussion. 



In the dipteron shown in figure 7, the liasistyle gs (basal 

 segment of the genital style) has remained in the condition typical 

 of the basal segment of the style in the lower forms, but the 

 dististyle h (distal segment of the genital style) becomes differ- 

 entiated into an apical appendage a (the apicappendix) and a 

 subapical appendage sa (subappendix). In the dipteron shown 

 in figure 36, the apical a]:)pendix a has become detached from 

 the subapical appendix .sa, and the process has been carried still 

 further in other forms. The apical appendix a of figure 7 

 apparently represents the apical portion a of the distal segment 

 of the genital style of the insects shown in figures 6 and 9, while 

 the subapical appendage .sa of figure 7 apparently corresponds 

 to the subapical process sa of the distal segment of the genital 

 style of the insects shown in figures 6 and 9, and it is onlj' by 

 comparing the parts in the Diptera and related Mecoptera, 

 that we are able to reach an approximately correct interpretation 

 of these parts in the higher forms. 



In the dipteron shown in figures 10 and 12, the basistyle gs 

 (basal segment of the genital style) becomes bent inward, and 

 the inflexion of the segment partially divides it into two secon- 

 arily-formed subdivisions or pseudosegments, and in the dip- 

 teron shown in figure 12, all that is left of the true distal segment 

 (dististyle) of the genital style is represented by the apical and 

 subapical appendages. In the dipteron shown in figure 11, the 

 basal and distal segments of the genital styles are greatly modi- 

 fied, the basal segment being represented by the i)late labelled 

 gs, while the distal segment h has developed vai-ious outgrowths 

 and other modifications which tend to mask its true character 

 as a distal segment of the genital stylo. In the syrphid shown 

 in figure 22, the distal segment h of the genital style is flat and 

 broad, while the basal segment gs is more membranous, and 

 becomes quite closely a))i)lie(l to the i)leural region of the ninth 

 abdominal segment. 



