OF WASHINGTON. 101 



In Acridiidae and Locustidje the microthorax is rudimentary, 

 consisting of only two or three small sclerites on each side of 

 the neck. In Blattidae and Gryllidas it is well-developed. 



The prothorax generally has an undivided notum, curved 

 downward on the sides, partially or almost entirely, crowding 

 out the pleural sclerites. In the Acridiidae it is marked by 

 three transverse grooves externally and three corresponding 

 ridges internally. This, as already shown, is due simply to the 

 assumption of the pleural function by the lateral parts of the 

 notum. 



The propleurum is best developed in the Blattidae (fig. 8), 

 where all the parts are present that occur in the other segments 

 except the paraptera and wing process, but these are ex- 

 clusively wing accessories and hence not to be expected in any 

 prothorax. The pleural suture {PS) is prominent and the 

 epimerum {Epm), the plate usually suffering most from the 

 encroachment of the notum, is actually larger than the epi- 

 sternum (Eps). Both katopleure (K) and trochantin (T) are 

 well developed. 



The mesothorax and metathorax are usually so similar that 

 separate descriptions are not necessary. The principal differ- 

 ences that occur between them are in the notal plates but these 

 are correlated with modifications of the wings. A very gen- 

 eralized adult notum is that oi Blattella germanica (figs. 6 and 

 7). The anterior and posterior marginal thickenings {k and /) 

 are simple. The posterior is folded forward on the ventral 

 surface forming a reduplication {Rd) and consequent free 

 posterior edge. The lines (fig. 6, o and /) apparent on the 

 surface are simply the external marks of the apodemes (fig. 7, 

 o and /). 



The mesopleura and metapleura are sufficiently illustrated 

 in their more generalized forms by Ischnoptera hyaliiia (fig. 

 3), Byrsotria fiimigata (fig. 5), and Spodromaiitis guttata 

 (figs. 2 and 4). In the Blattidae only one parapterum is pres- 

 ent. Figs. 4 and 5 show the internal surfaces with heavy 

 pleural ridge (PR) and prominent pleural apodeme (PA) 

 present in each case, with the wing process (WP) at one end 

 and the coxal process (Cx P) at the other end of the ridge. 

 Though the blattid epistemum is irregular in shape and some- 

 what subdivided by incomplete lines, yet it can be unmistakably 

 identified by its relation to the pleural suture and pleural ridge. 

 In the Acridiidae the trochantin is absent or rudimentary and 

 the katopleure is fused with the episternum. 



