NO. 6 INSECT ABDOMEN — SNODGRASS 9I 



The basal plates of the second gonopods in the male may unite with 

 each other and with the primary sternum of their segment, as do those 

 of the preceding segments, to form a composite zygosternum, and in 

 such cases the styli either retain the typical shape of styliform organs, 

 or they are lost. The gonapophyses, usually termed the parameres, 

 however, in the more generalized insects, are associated with a median 

 intromittent organ, or penis (figs. 33 B, 39 D, Pen), which is a tubular 

 evagination of the segmental wall behind the ninth sternum, bearing 

 the opening of the ejaculatory duct at its extremity. In the higher 

 insects the primitive penis becomes partly or entirely suppressed, and 

 the parameres unite with it or with each other to form the secondary 

 and often more complicated intromittent organ usually termed the 

 aedcagus (fig. 39 E, Acd), which incloses the ejaculatory duct and 

 bears the gonopore. 



The basal plates of the gonopods of the ninth segment in the male, 

 if not completely amalgamated with the sternum, may form free lobes 

 of the ninth segment, or they may unite with each other, with the 

 sternum, or with the sternum and the tergum of the ninth segment. 

 In this way the genital segment of the male, especially in holometa- 

 bolous insects, assumes a great diversity of structure, and it is often 

 reduced to a simple continuously sclerotized annulus. The ninth seg- 

 ment, however, regardless of its form, always bears the aedeagus, 

 which may be partly or wholly concealed in a genital chamber of its 

 ventral part, and it generally carries clasping organs of various forms 

 on its posterior margin. Usually, among the clasping organs of the 

 ninth segment, or often the only structures having a clasping func- 

 tion, is a pair of lobes flexible at their bases and independently mov- 

 able by muscles taking their origins in the basal plates of the gonopods, 

 or in the regions of the ninth annulus derived from the gonopod bases. 

 These movable claspers, designated the harpes by students of Lepi- 

 doptera, are evidently the homologues of the styli of the more general- 

 ized insects (fig. 39 D, E, Sty). 



It is most important, now, to observe that in the fundamental or- 

 ganization of the gonopods there are only two sets of appendicular 

 structures that are independently movable by muscles inserted directly 

 on their bases. These structures are the styli and the gonapophyses. 

 Therefore, in the ninth segment complex of the male genitalia, there 

 will generally be two sets of appendicular structures, the harpes and 

 the parameres, provided with muscles arising in the basal plates of 

 the gonopods, or in the parts of the ninth segmental ring derived 

 from the latter. By a study of the genital musculature, then, these 

 two structures can be identified with certainty in almost all cases 



