y2. SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



Rudiments of appendages have been shown by Heymons (1897) 

 to be present on each of the first lo segments of the abdomen in the 

 young embryo of Lcpisma saccJmrina. With the dorsal growth of 

 the embryonic walls, however, the appendage rudiments become 

 gradually flattened, until finally they form the lateral parts of the 

 definitive abdominal sterna. The styli of Lepisma, Heymons says, 

 are not developed until a long time after hatching, but when they do 

 appear they arise as outgrowths from the parts of the ventral body 

 wall derived from the embryonic appendages. 



In the Diplura the styli are small if present (fig. 24 C) and are 

 borne by the sternal plates of the segments; but the stylus-bearing 

 areas (Cxpd) of each sternum may be demarked from the true ster- 

 nal area (Stn), and upon them arise the muscles of the styli (D). 

 From this condition it is then only another step to that in which the 

 ventral sclerotization of a segment becomes unified in a definitive 

 sternal plate showing no evidence of its coxosternal origin, except 

 for the possible retention of the styli. 



On the genital segments of some species of Thysanura a slender 

 process arises at or on the inner dorsal angle of the base of each 

 coxal plate (fig. 24 F, G, iGon, 2Gon). These four processes may 

 be termed gonapophyses because those of the female, which form an 

 ovipositor in Thysanura, are without doubt homologous with the 

 ovipositor blades so named in other female insects. The gonapophyses 

 of the ninth segtnent in male Thysanura are closely associated with 

 the penis (G, sGon) and are often termed parameres because they 

 are supposed to correspond with accessory genital structures called 

 parameres in other male insects (see Heymons, 1897). The term 

 " paramere ", however, has been given to many different processes 

 of the genital complex in pterygote insects, and it is not certain that 

 any of them is a true gonapophysis. Heymons has shown that the 

 genital processes of Lcpisma are formed as outgrowths from the 

 inner margins of the coxal plates of the eighth and ninth abdominal 

 segments. " Gonapophyses " may be defined, therefore, as mesal 

 processes of the bases of the gonopods ; they would appear to be coxal 

 endites specially developed on the appendages of the genital segments. 

 In the Thysanura each gonapophysis is provided with small muscles 

 arising on the supporting coxal plate (F). 



The intromittent organ of male Thysanura consists of a median 

 tubular penis, or phallus, arising from the venter of the ninth abdomi- 

 nal segment between the bases of the coxal plates of this segment 

 (fig. 24, E, G, Pen), where it is closely embraced by the second 

 gonapophyses if these processes are present (G). The organ appears 



