1919] Walker: Structure of Orthopteroid Insects 309 



Odonata. 



The form of the terminal segments ot the dragonflies recalls 

 the Phasmids, as suggested by Crampton, there being no 

 abbreviation, but on the contrary, an elongation of all of them, 

 as compared with the usual conditions. A fully developed 

 ovipositor is present in all of the suborder Zygoptera and some 

 of the Anisoptera (Aeshnidas: — Aeshnins and Petalurina?) , 

 while a more or less reduced and simplified one occurs in the 

 other groups. This ovipositor is remarkable in several ways. 

 The dorsal valvulas are broad, subtriangular, hood-like at the 

 apices, and form a pair of flaps or covers for the ventral and 

 inner valves, these structures serving as the actual instrument 

 for making the punctures or incisions in which the eggs are 

 placed. They thus resemble closely the broad sternal processes 

 of segment nine in Lepisma, Machilis and other Thysanura, 

 which cover over the two pairs of valvular (representing the 

 ventral and inner pairs) in quite a similar manner. They are 

 still more interesting in the fact that they retain the styli in 

 adult life as functional sense-organs, the Odonata being the 

 only Pterygote order in which this is the case. 



The ventral valvulas also possess well developed basivalvulae, 

 the dorsal valvulas superior and inferior apophyses. A superior 

 interval vula and intervalvular membrane are also present, but 

 no inferior valvula, the strong rami of the inner valvulae being 

 articulated with the inferior apophysis. 



There is also a valvifer, having typical connections with 

 the valvulae and ninth tergal apodeme. 



The occurrence of these features in the Odonata is of interest 

 in showing that they must be characters of very ancient origin 

 and are in no way specially characteristic of Orthopteroid 

 groups. 



