INSECT ABDOMEN SNODGRASS 



39 



invariably take their origin on the eighth tergum (fig. 9) ; the dorsal 

 muscles of the second valvifers arise on the ninth tergum. 



From this sketch of the more generalized structure of the ovipositor 

 in pterygote insects it is clear that the organ may be derived theoreti- 

 cally from a pair of genital appendages having the same structure and 

 the same relations to the eighth and ninth segments of the abdomen 

 as have the female gonopods in the Thysanura. Thus we may con- 

 ceive that the parts of the pterygote ovipositor belonging to the 

 eighth segment (fig. 10 A) represent the limb bases (LB) of a 

 pair of gonopods, which become the first valvifers (B, iVlf), and 

 a pair of corresponding gonapophyses (A, Gon), which become the 

 first valvulae (B, iVl). The styli of the first gonopods (A, Sty) are 



GprLB(iVlf) 3 



Fig. 10.— Analytical diagrams of the morphology of the pterygote ovipositor. 



A, ventral view of theoretical generalized structure of eighth segment and 

 gonopods (cf. fig. 6 E, fig. 7 A). 



B, lateral viev^r of generalized eighth segment and first gonopod ; stylus absent 

 in all pterygote insects. 



C, lateral view of generalized ninth segment and second gonopod; basis of 

 gonopod {LB) subdivided into second valvifer {2VIJ) and third valvula {3VI), 

 stylus {Sty) sometimes present. 



absent in all pterygote insects (B). The gonopore (A, Gpr) is located 

 typically behind or above the posterior margin of the primitive sternum 

 of the eighth segment {Stn), but between the proximal ends of the 

 limb bases. It is, then, but a secondary matter if the limb base plates, 

 or valvifers, of the eighth segment become more or less dissociated 

 from the eighth segment (B) and variously connected with the ninth 

 tergum or with the second valvifers. As above noted, the first valvi- 

 fers, regardless of their displacement, retain their muscle connections 

 with the eighth segment. The parts of the pterygote ovipositor be- 

 longing to the ninth segment may be supposed in the same way to 

 represent corresponding parts of the second gonopods of Thysanura, 

 the second valvifers (fig. 10 C, sVlf) being limb bases, and the second 

 valvulae {2VI) the second gonapophyses. 



