42 PROC. V ENT. SOC. WASH., VOL. 20, NO. 3, MAR., 1918 



The furcasternum is connected with the pleural region by a 

 post-coxal bridge (fig. 14, po) in many adult insects, and in cer- 

 tain Apterygota (fig. 12, po). This postcoxal bridge is retained 

 in but few larvae, such as those of the Pyrochroids (fig. 7, po), 

 although in the larva of Corydalis, there is found a postcoxal 

 plate (fig. 4, po) which is homologous with the postcoxal bridge. 

 This region is not chitinized in the larva of Dytiscus, but is rep- 

 resented by a membranous fold behind the coxa (fig. 3, po). 

 Behind the postcoxal region, two internal parapophyses for muscle 

 attachment, are found. Their position is indicated externally 

 by pits, as in figure 4, p, or by small sclerites as in figure 3, p. 



The arm of the furca, or internal apophyses, may be united 

 with the apodeme, or internal ridge of the pleural region; but 

 when this is not 'the case, the furcal arm is usually attached to 

 the apodeme of its side of the body, by the furco-apodemal 

 muscles; and the furco-postscutellar muscles extend between it 

 and the postscutellum, as shown by Voss, 1904, in the thorax of 

 Gryllus. The furca of the prothorax is attached to that of the 

 mesothorax by the profurco-mesofurcal muscles, and the furca 

 of the mesothorax is similarly attached to that of the metathorax 

 by the mesofurco-metaf urcal muscles (the prefixes pro-, meso-, 

 and meta-, being used to indicate whether the structures between 

 which the muscles extend, are in the prothorax, mesothorax, or 

 metathorax respectively). The spina, or unpaired median apo- 

 physis, is connected with the furca of its own segment by the 

 spina-furcal muscles in some insects, and the spina of one seg- 

 ment is usually connected with the furca of another segment by 

 the prospino-mesof urcal or by the mesospino-metaf urcal and 

 mesospino-prof urcal, etc. (the prefixes being used to indicate 

 the segment in which the structure to which the muscles are at- 

 tached, is located). As shown by Voss, 1904, in GryUus, the tro- 

 chantero-furcal and the coxo-furcal muscles extend from the 

 trochanter and coxa to the furca, and, with the other muscles 

 mentioned above, serve to identify the furcasternal region when 

 they are retained. The basisternum and furcasternum are fre- 

 quently united, but are usually separated by a suture. When 

 not otherwise demarked, the furcasternum may be regarded as 

 that region somewhat between and behind the coxae, as in figure 

 3, fs, although in this case, the furcasternal region is indicated 

 by the furcal pits /, and is separated from the sternite behind it 

 by a crease, as indicated by the dotted line. 



The fifth sternal plate, found in the prothorax of such insects 

 as Capnia (fig. 14, pfs) is present in but few insects as a distinct 

 plate. It is doubtless united with the region behind it in larval 

 insects. 



