6 Annals Entomological Society of America [Vol. XV, 



it is vestigial or absent and its place is taken by the 10th tergum. 

 The cerci, when not modified as claspers in the male, are usually 

 similar in the two sexes. 



The 8th sternum* is unmodified in the male, as it does not 

 underlie the genital aperture, but the 9th sternum is generally 

 much enlarged and is usually termed the subgenital plate, as 

 it occupies a position in relation to the genitalia analogous to 

 that of the 8th sternum in the female. As this implies a 

 homology that does not exist, the term "hypandrium"t has 

 been recently proposed by Crampton for the male subgenital 

 plate. He does not, however, use it in a strictly morphological 

 sense, but to designate the terminal ventral sclerite, whether 

 this represents the entire sternum or only a part. When the 

 9th sternum, e. g., is transversely divided, as in the Ephemerida 

 and the Acrididae, it is the distal part only that is called the 

 hypandrium, but when it is undivided, as in most Orthoptera, 

 Blattoidea, Mantoidea, etc., the entire sternum becomes the 

 hypandrium. As thus used the term is therefore open to 

 objection, as it tends to obscure the homologies of the parts 

 concerned, although it is a convenient one to retain for descrip- 

 tive purposes. 



The 9th sternum is primitively divided into three plates, a 

 basal sternite and two disto-lateral coxites, each of the latter 

 bearing a terminal stylus. This primitive condition is well 

 exemplified by GryUoblatta, especially in the immature stages 

 (PI. VII, Fig. 66) and certain Ephemerida, such as Blast uriis 

 nebiilosiis (PI. I, Fig. 2), although in the latter the styli (or coxites?) 

 are secondarily segmented. In most Ephemerida, however, the 

 coxites are fused but remain separate from the sternite, so that 

 the former have the appearance of another sternum (coxale) 

 and have, in fact, been mistaken for the 10th sternum (Eaton, 

 '88; Morgan, '13). A similar structure is met with in the 

 Phasmoidea and Acridoidea, except that in these groups the 

 styli are wanting. In most groups, however, the sternum is a 

 single large plate, with or without styli, which when present 

 are borne at the distal margin of the plate. Such a sternum 

 thus consists of the united coxites and sternite and has therefore 



* I. e., the sternum of the 8th abdominal segment; in reality it is generally 

 the 7th actual abdominal sternum. 



t Incorrectly described as the "ventral portion of the tenth abdominal 

 segment." (Crampton, '18, p. 50). 



