1922] Walker: Structure of Orthopteroid Insects 21 



In R. carbonaria Sauss., the only species I have examined, the 

 9th tergum, is the only one that is divided. The 10th and 

 supra-anal plate are both of large size, though somewhat 

 sulcate and weakened mesially. The 9th sternum forms a 

 large, somewhat convex hypandrium, and is almost completely 

 fused with the tergum. The cerci are simple and styliform 

 with a distinct basipodite. Just beneath each is a chitinous 

 hook, which apparently belongs to the paraprocts, but is 

 perhaps developed from the cereal basipodite. It is also shown 

 in de Saussure and Zehntner's figure of R. cyanipennis (op. cit., 

 PI. XVII, Fig. 34). The long processes of the paraprocts in 

 R. carbonaria Sauss. and R. forceps Sauss., are remarkable 

 for their modification as copulatory forceps. They are long 

 and stout, with thickened apices, abruptly bent inwards. 



In R. mexicanus Sauss., according to the figure of de Saussure 

 and Zehntner (1. c, PI. XVII, Fig. 30), the cerci are indistinctly 

 divided into nine segments, but it seems probable, on comparison 

 with other species, that this segmentation is not a primitive 

 condition. In this species and others, such as R. cyanipennis 

 Sauss., the processes of the paraprocts are not modified to 

 serve as claspers. 



AcRiDOiDEA. In the locusts the hind margins of the last 

 two or three abdominal terga are increasingly oblique caudad, 

 this obliquity being associated with a marked shortening of 

 their mid-dorsal lengths, as compared with their lateral margins. 

 These features, together with the large, more or less upcurved 

 ninth sternum, result in a general upturning of the end of the 

 abdomen, the opening of the genital cavity facing dorsad 

 instead of caudad. In respect of the shortening and obliquity 

 of the terga, the group may be compared with the Tridactyl- 

 oidea, the resemblance to which is greatest in the Acrydiidee 

 (Tettigidse), but is even here not very marked. 



The segments are all separate in the Acrydiidas, but in the 

 Acrididce the 9th and 10th terga are laterally fused, as in the 

 females. A median furcate appendage, the furcula, is sometimes 

 borne by the latter, as in Melanoplus. The large, usually 

 triangular supra-anal plate is primarily divided by a trans- 

 verse suture, as in the female (see Part I), but in the adults 

 this division is frequently lost.* The peculiar subdivision of 



* Chopard ('20) has given good reasons for considering this transverse suture 

 to be the true boundary between the 9th and 10th terga, the apparent boundary 

 being a secondary ridge. 



