The Basal Sclerites of the Leg in Insects. 5 



portion of the episternum, together with the trochantin, and the 

 narrow marginal region ac (Figs. 1, 2 etc.). 



It is apparent from the foregoing discussion, that the trochantin 

 may unite with the lower portion of the pleural plate, to form a 

 compound sclerite ptn (Figs. 13 and 8) marked oif by a well defined 

 suture extending to the pleural suture g. If this suture (marking off 

 the region pin) were continued backward beyond the pleural suture, 

 it w^ould demark a region composed of the trochantin, etc., together 

 with the lower portion of the pleural plate, and would correspond 

 roughly to the combined sclerites ptn and hem of Fig. 13. If this 

 composite region, consisting of the trochantin and the lower portion 

 of the pleural plate, were to become detached to form a distinct 

 plate, we would have a condition similar to that represented in the 

 plate designated as pst (Fig. 21) in the prothorax of the stonefly 

 Perla. In the meso- and metathorax of this insect, the base of the 

 trochantin is completely and indistinguishably fused with the lower 

 portion of the pleural plate, so that it is not surprising that the 

 lower portion of the pleural region would remain united with the 

 trochantin, when the latter became detached, in the prothorax, to 

 form the composite region pst. The location of the plate pst (Fig. 21) 

 with reference to the pleural coxal fulcrum (at the bottom of the 

 pleural suture) clearly shows that this plate comprises an area of 

 much greater extent (posteriorly) then the trochantin {tn of Figs. 2, 

 3, and 22) alone. Furthermore, the fact that the composite sclerite 

 pst (Fig. 21) contains the lower portion of the pleural suture (which 

 is not continued down into the coxa, in this case) clearly shows that 

 the lower portion of the pleural region has become detached from 

 the remainder, and has united with the trochantin to form the 

 plate pst. We have therefore designated the plate pst of Fig. 21, 

 as the "pseudo-trochantin", to indicate that it is not strictly homo- 

 logous with the trochantin alone (i. e. tn, of Figs. 2, 3, and 22). 



It is very probable that the plate pst of Fig. 21, is homologous 

 with the plate labeled pst in the thorax of Eosentomon (Fig. 20). If 

 this is true, the plate usually designated as the trochantin alone, 

 in the apterygote insects, is in reality a "pseudo-trochantin". 



The sclerites ac and sc, found in the metathorax of the grass- 

 hopper Dissosteira (Fig. 16) are sometimes mistaken for the trochantin; 

 but the sclerite designated as ac in Fig. 16 is homologous with the 

 sclerite ac of Fig. 2, called the antecoxal piece, or antecoxale, while 

 the sclerite sc of Fig. 16 is a new formation marked off in the 



