1919] Walker: Structure of Orthopteroid Insects 313 



Embiidina — Segments seven to nine unmodified, there being 

 no specialized subgenital plate; ovipositor wholly absent; 

 supra-anal plate practically absent, replaced by the large tenth 

 tergite; paraprocts lobate, unchitinized; cerci two-jointed. 



Plecoptera — Eighth sternum generally more or less modified 

 to form a subgenital plate, sometimes with a pair of lobes or 

 processes, possibly representing vestigial ventral valvulae; 

 ovipositor otherwise absent; ninth sternum horizontal, unmodi- 

 fied; ninth and tenth segments tending to be annular; supra- 

 anal plate variable, sometimes covered by a prolongation of 

 the tenth tergite; cerci typically long and many- jointed, their 

 basal segments fused with the large paraprocts. 



Comparison of Ovipositors of Pterygote and 

 Apterygote Insects. 



In the Apterygota the ovipositor is present only in the 

 families Machilidae and Lepismatidae of the order Thysanura. 

 It consists of two pairs of filiform gonapophyses, arising from 

 the eighth and ninth sternum respectively. In Machilis sp., 

 e. g., the separated eighth sternum has the appearance shown 

 in Fig. 74. It is deeply bilobed, each lobe bearing a stylus 

 while the gonapophyses occupy a median position between the 

 lobes. They are very long and flexible and are divided by faint 

 constrictions with numerous segments, with regularly arranged 

 groups of setas. The ninth sternum (Fig. 75) is similar to the 

 eighth, except that the styli and sternal lobes are much longer, 

 while the gonapophyses are shorter and more slender. In the 

 natural position they reach about the same distance back. 

 As compared with the eighth and ninth sterna, the preceding 

 sterna (Fig. 73) differ not only in the absence of gonapophyses, 

 but in the union of the stylus-bearing lobes and the presence of a 

 triangular basal plate (ste), these parts being separated only 

 by sutures. They also differ in the presence of eversible 

 glands (cgl). 



It is now generally recognized that the basal plate is the true 

 sternite, while the lateral styli-bearing plates are coxites, 

 these probably representing flattened coxae of abdominal limbs 

 which have otherwise disappeared (Haase, '89).^^ The sterna of 



"Haase, Erich, Morph. Jahrb., Vol. XV, pp. 331-435, Pis. XIV, XV (1889); 

 Verhoeff. Zool. Anz., Vol. XXVI, pp. 60-77 (1903). 



