NO. 6 INSECT ABDOMEN — SNODGRASS 'J'J 



of the body wall from behind the region of the ninth sternum, having 

 the opening of the ejaculatory duct at its extremity. 



The thysanuran gonopods contain, in their simplest form, the 

 fundamental elements of the organs of copulation and oviposition of 

 pterygote insects. In the male the gonapophyses of the second gono- 

 pods become the so-called parameres of the copulatory apparatus ; in 

 the female, the first and second gonapophyses become the first and 

 second valvitlae of the ovipositor, and the basal plates of the second 

 gonopods form the third valvitlae, when the last are present. 



The uropods, or cerci, of the Thysanura are typically long, multi- 

 articulate filaments (fig. 7 A, Ccr) borne by the eleventh segment 

 (B, XI). In the Dicellura the abdomen contains only 10 segments, 

 and the uropods, therefore, in this group appear to belong to the 

 tenth segment. They are filamentous in Campodea, styliform in 

 Projapygidae, and take the shape of large pinchers in Japygidae (fig. 

 40 C, Cer). The uropods differ from the preceding appendages in 

 that they are not differentiated into a basal plate and a stylus, and 

 they bear neither eversible sacs nor processes corresponding with 

 the gonapophyses. 



THE ABDOMINAL GILLS OF EPIIEMERID LARVAE 



The abdominal gills of ephemerid larvae, together with the lateral 

 lobes of the body wall supporting them (fig. 34 A), appear to be ap- 

 pendages of a more primitive form than the abdominal appendages 

 of the Thysanura. Their structure, with certain modifications, is 

 repeated in the abdominal appendages of several groups of holometab- 

 olous larvae ; but it does not furnish the basis of the structure of 

 the gonopods in adult pterygote insects, which, as already stated, 

 is to be derived from that of the gonopods of the Thysanura. 



The ephemerid larval gills have various shapes, some being taper- 

 ing stalks, either single or double, fringed with filaments (fig. 34 A, B, 

 Hrn), while others are expanded into broad plates; but, whatever the 

 form, each organ is movably attached by its base to a large lateral 

 lobe of the body wall (LB). The gill is movable by muscles arising 

 in the ventral part of the supporting lobe (A, B, binds). 



The gill-bearing lobes are not movable, since there are no body 

 muscles inserted upon them. The vertical lateral muscles of the 

 abdominal segments extend from the tergum to the edge of the ster- 

 num mesad of the gill lobes (fig. 15 A, //, 2I, ^l, fig. 34 A, /). The gill- 

 bearing lobes therefore have the character of limb bases implanted 

 in the pleural areas of the segments between the tergal and sternal 



