32 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



2. The gonapophyses are continuous with the mesal proximal angles 

 of the basal plates, and each is provided with a short muscle arising 

 on the supporting plate. 



3. The basal plates of the ovipositor are evidently the bases of the 

 appendages (gonopods) of the eighth and ninth abdominal segments. 

 Each bears a gonapophysis proximally and a stylus distally, and is 

 equipped with dorsal muscles arising on the tergum of its segment. 



4. The styli of the thysanuran gonopods do not form a part of the 

 ovippsitof , but serve to support the end of the abdomen, and are active 

 in the locomotion of the insect. Each is movable by muscles arising 

 proximally in the basal plate on which it is borne. 



IV. GENERAL STRUCTURE OF THE PTERYGOTE OVIPOSITOR 

 AND ASSOCIATED ORGANS 



There appears to be little doubt that the pterygote ovipositor is an 

 organ formed of the appendages of the eighth and ninth abdominal 

 segments, and that it is, therefore, homologous with the ovipositor 

 of the Thysanura. If, in the embryonic development, the blades 

 of the pterygote ovipositor appear to arise directly from the ventral 

 walls of the genital segments, it is probable that the apparent venter 

 of each segment includes the areas of the limb bases and the sternum. 

 In the definitive condition the limb bases are always distinctly dififer- 

 entiated from the sterna. Associated with the base of the ovipositor 

 are typically three internal organs formed by median invaginations 

 of the ectoderm. The first is the median oviduct, the second is the 

 spermatheca, the third is a pair of accessory glands. Finally, there 

 may be formed cavities at the base of the ovipositor, covered by 

 a posterior extension of the eighth sternum, and of the seventh 

 sternum. These cavities are the genital cliamher above the eighth 

 sternum, and the vestihulum above the seventh sternum. 



THE GENITAL INVAGINATIONS 



The three median genital invaginations of female insects, namely, 

 the oviduct, the spermatheca, and the accessory glands, have anatomi- 

 cally metameric relations to one another, since primarily they are de- 

 veloped on successive segments (fig. 8 A) ; but it has not been shown 

 that there is any morphological significance in this fact. 



The oviductus communis, as shown in section II, first appears in the 

 embryo, nymph, or larva of many insects as a median ingrowth on the 

 posterior part of the venter of the seventh abdominal segment, or in 

 the intersegmental membrane between the seventh and eighth sterna. 



