1922] Walker: Structure of Orthopteroid Insects 15 



apodeme (map). The supra-anal plate (Fig. 16) consists of a 

 pocket, whose walls are partly membranous, partly differen- 

 tiated into separate sclerites, which are moved by intrinsic 

 muscles (vide Smith, op. cit.) On each side of the opening 

 of the sac is a somewhat triangular plate, termed by Smith the 

 para-genital plates (pg) which seem to be the homologues of 

 the two dorsal basal parts of the supra-anal plate of Capnia. 

 In the mouth of the sac can be seen a median chitinous hook 

 (mst) and a pair of lateral rods or styles (1st). These are 

 termed by Smith the median and lateral stylets. They are all 

 connected at base with a strong bar, which bounds the sac in 

 front and joins the base of the median apodeme of the tenth 

 tergum. The copulatory hook, or median stylet, is the "titil- 

 lator" of other species, of such genera as Arcynopteryx and 

 Skoheleva (Klapalek, '12), in some members of which it has the 

 form of a long slender spine. 



The supra-anal plate is subject to still other modifications, 

 such as, e. g., in Acroneuria hrevipennis (Crampton, 'IS), in 

 which it bears a pair of well-developed hooks, while in other 

 forms, such as Isoperla sp. (PI. II, Fig. 18) it is wholly without 

 special modifications, and even imperfectly differentiated. 



As it is evident that these modifications have developed 

 within the order, no attempt need be made to homologise them 

 with similar structures found in other orders. Crampton ('18) 

 has compared the appendage of the supra-anal plate (sperm- 

 conveyor) of Capnia to the slightly similar horn-like projection 

 of the tenth tergum in certain Odonata (Ischnura) and remarks 

 that although not strictly homologous "it is unnecessary to 

 apply different names to the two structures, which are prac- 

 tically the same in their nature and position on the tergal region 

 of the segment bearing them." So far from being "practically 

 the same," they are not only borne by different segments, but 

 are adapted to wholly different functions, that of Capnia being 

 a sperm-conveyor, while that of Ischnura is a brace which fits 

 upon the mesosternal lamina of the female in copulation. 

 Crampton also labels the furcate appendage of the supra-anal 

 plate of Scudderia furcata Brunn. with the same abbreviation 

 as he uses for the structures just mentioned, though this is 

 also quite different in nature from either of the others, being a 

 development within the Tettigoniid subfamily Phaneropterinae. 



