NO. 8 



INSECT ABDOMEN SNODGRASS 



65 



(indicated by the curved arrow on the right), and this movement 

 bears down on the second valvifer and gives this valvifer a thrust 

 posteriorly, which causes the dorsal valvula to slide backward on the 

 ventral valvula while the latter is moving forward. The opposite 

 movement of the first valvifer (indicated by the curved arrow on 

 the left) reverses the movement of the valvulae on each other. Thus, 

 by a simple rocking motion of the first valvifer on its articulation 

 with the ninth tergum, the two valvulae of the same side move length- 

 wise on each other alternately in opposite directions. This action can 

 easily be demonstrated on a dissected specimen. But also it will be 

 observed that a rocking motion of the second valvifer on its articu- 

 lation with the first valvifer (dh) imparts the same movements to 



iVlf 



■ A 



2Vlf 



iVl 



Fig. 21.— Diagrams of the basal mechanism of the ovipositor of Gryllus 

 assimilis. 



a, articulation of first valvifer with ninth tergum; aiv, anterior intervalvula ; 

 c, attachrnent of first valvula to first valvifer; dh, inner articulation between 

 first and second valvifers ; e, anterior apodeme of first valvifer ; /, posterior 

 apodeme of first valvifer ; g, anterior apodeme of second valvifer ; i, posterior 

 apodeme of second valvifer; k, median apodeme of posterior intervalvula; piv, 

 posterior intervalvula; iVl, first valvula; 3VI, third valvula; iVlf, first valvifer; 

 2Vlf, second valvifer. 



the two valvulae, and increases the degree of movement in the dorsal 

 valvula. The mechanism is extremely delicate, and the least motion, 

 either of the first valvifers on the ninth tergum, or of the second 

 valvifers on the first valvifers, produces the sliding movement of the 

 valvulae on each other. The dorsal valvulae are the stronger of the 

 two pairs of blades forming the shaft of the ovipositor, and end in 

 sharp points which normally project beyond the thin, truncate tips of 

 the second valvulae (fig. 17 B, C). 



The muscles that bring about the movement of the valvulae on each 

 other are the three pairs of large lateral muscles inserted on the 

 valvifers (fig. 17E, H, j, 6, /). These muscles, morphologically, are 

 the tergopleural muscles of the eighth and ninth abdominal segments. 

 The first on each side (3), arising on the eighth tergum and inserted 



