4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



bears an eversible or retractile sac having various functions, repre- 

 sented by the vesiculae of Thysanura, the gill-bearing lobes of certain 

 neuropterous larvae, and the plantar lobes of caterpillars and sawfly 

 larvae. The basis of an abdominal limb usually takes the form of a 

 lobe or plate of the body wall, and in the pregenital segments the 

 limb bases are generally united with the sterna in adult msects. The 

 appendicular process of the basis more commonly present is the 

 stylus of the lower insects, or its derivatives, including the clasper- 

 like organs borne by the male gonopods of the higher insects. The 

 other limb process is the gonapopJiysis, which occurs only on the 

 gonopods. Both the styli and the gonapophyses may l^e movable by 

 muscles arising within the supporting basal lobes or plates, or on 

 segmental areas derived from the latter. 



7. No positive evidence can be adduced from the known facts of 

 anatomy or embryology to establish the homology of either the stylus 

 or the gonapophysis. Many structural interrelations, however, sug- 

 gest that the stylus is the telopodite of the appendage, and that the 

 gonapophysis is an endite process of the basis. 



8. The genital appendages, or gonopods, have the same essential 

 structure as the appendages of the pregenital segments. Their dis- 

 tinguishing feature is the presencq of the gonapophyses arising 

 mesally from the bases. In the female, the gonapophyses of the two 

 pairs of gonopods form the first and second pairs of valvulae of the 

 ovipositor ; in the male the gonapophyses of the ninth segment be- 

 come the parameres. The styli of the gonopods are usually suppressed 

 in the female of pterygote insects ; those of the ninth segment of 

 the male form the movable claspers. or Jiarpcs. of the copulatory 

 apparatus in the Endopterygota. 



9. The bases of the gonopods in adult female insects become plates 

 supporting the first and second valvulae ; those of the second genital 

 segment may form a third pair of valvulae. In the male the bases of 

 the single pair of gonopods often form distinct pleural plates of the 

 ninth segmental wall between the tergum and the sternum, or they 

 may fuse with either the tergum or the sternum, or with both ; again 

 they may unite with each other to form a plate either coalesced with 

 the sternum or free and independently movable behind the latter. 



10. The parameres of the male are associated with the median 

 penis in the lower insects, generally uniting with the latter except 

 in Thysanura ; but the penis may be suppressed, and the |)arameres 

 then unite with each other -and inclose the terminal part of the 

 ejaculatory duct to form the more complex copulatory organ known 

 as the aedeagiis. The parameres are to be identified throughout the 



