NO. 6 GRASSHOPPER ABDOMEN SNODGRASS 6l 



VI. THE EXTERNAL MALE GENITALL\ 



The external genital structures of the male are so different in the 

 grasshoppers from these organs in other Orthoptera that little attempt 

 will be made here to establish homologies between the acridid organs 

 and the various types of genital structures found in the other orthop- 

 teroid families. Walker (1922) has presented a plausible though 

 theoretical scheme for tracing the evolution of the male organs in 

 the Orthoptera, and his ideas will be discussed in a future, more 

 general paper. The acridid genitalia have been but little studied from 

 a comparative standpoint, and only one writer (Hubbell, 1932) has 

 attempted to make use of their characters for taxonomic purposes. 

 The basic structure of the organs is surprisingly alike throughout the 

 family, but there can be no doubt that distinctive specific variations 

 are well marked in many cases. 



GENERAL STRUCTURE OF THE MALE GENITALL\ IN ACRIDOIDEA 



The terminal part of the adult male abdomen in both Acrididae and 

 Tetrigidae is characterized by a great enlargement of the ninth ster- 

 num, and by a partial or complete separation of the latter into a 

 proximal part and a distal part that are more or less movable on 

 each other (figs. 27 A, 33 A, 35 A, 36 B, 39 A, IXS, IXSL). The 

 proximal sternal plate (IXS) may be designated the ninth sternum 

 proper; the distal lobe (IXSL) is the male subgenital plate. Styli 

 are absent in all Acridoidea, but if they were present on the ninth 

 abdominal segment they undoubtedly would be carried by the genital 

 lobe of the sternum, and for this reason the lobe is sometimes re- 

 garded as representing the united coxopodites of the ninth segment. 

 Since, however, in the young male nymph there is no suggestion of 

 the later division of the ninth sternum, it seems probable that the 

 two sternal plates of the adult are the result of a secondary subdivision 

 of the usual coxosternum of the ninth segment without reference to 

 its more primitive composition. 



The subgenital lobe of the ninth sternum is usually turned upward 

 on the end of the proximal plate, and its dorsal margin may be tightly 

 closed against the lobes of the eleventh segment (figs. 29 A, 30 A, 

 34 A). More generally, however, there is continued forward from 

 the free margin of the subgenital plate a thick membrane, the pallium 

 (fig. 33 A, Pal), which presents a rounded or hoodlike dorsal surface 

 closing the space between the upper end of the genital plate and the 

 eleventh segment. Behind the latter the pallium is always deeply 

 inflected to form the posterior wall of the genital chamber (fig. 24 A, 



