1919] Walker: Structure of Orthopteroid Insects 285 



present, but is very small and sub-chitinized. The characteristic 

 rod (pap) is fully developed and is separate from the valvifer, 

 but its base of attachment is in very close relation to the latter; 

 in fact, in an internal view of the nymph, they appear to be in 

 contact with one another. 



The first appearance of this rod in the nymph of Melanoplus 

 is a slight invagination of the soft chitin at the angle between 

 the valvular bases. This is later continued cephalad as a thin 

 band-like tube, as seen in the last nymphal stage, assuming its 

 final form only at the last moult. No external appearance of 

 the valvifer is present in Melanoplus. 



In respect of the presence of a distinct valvifer in the 

 Acrydiidae we may consider the latter to be a more primitive 

 family than the Acrididae and this view is borne out by other 

 features of the terminal segments: In the nymph of Acrydium, 

 e. g., the ventral valvulae possess unmistakable basivalvulse 

 (bs), which, however, in the adult became divided into two 

 sclerites, a lateral and a ventral, the latter representing the 

 two principal ventral sclerites in Melanoplus. The ninth and 

 tenth tergites are quite separate and less reduced than in 

 Melanoplus, especially in the nymph. The tenth tergite 

 (Fig. 29) is imperfectly divided into median and lateral regions, 

 of which the former is less heavily chitinized and is produced 

 caudad into a lobe which divides the eleventh tergite into two 

 separate lateral plates. The supra-anal plate also shows two 

 lateral chitinized areas. In the nymph (Fig. 29), the eighth and 

 ninth tergites are unmodified, but in the adult they also present 

 a narrow, less densely chitinized median region, which folds 

 inwards, allowing the lateral parts to come together in a pointed 

 or Gothic arch. 



These peculiar features are very suggestive of the Tri- 

 dactylidae, which also resemble the Acrydiidae in some other 

 respects. The cerci are divided into a stouter basal part, 

 which is hairy, and a slender smooth apical part. This gives 

 them the appearance as though composed of two fused seg- 

 ments, a feature which is also suggestive of some Tridactylidae 

 (q. v.). 



In other respects the female genitalia closely resemble 

 those of the Acrididae, the larger size of the superior intervalvula 

 in Acrydium as compared with that of Melanoplus being perhaps 

 the most striking difference noted. 



