The Basal Sclerites of the Leg iu Insects. 7 



is "dicoxal", or is divided into an anterior and posterior region vc 

 and me (Figs. 2, 3, 4, 5, 6, 7, 8. 12, 14, etc.) by the coxal suture I, 

 which is merely a ventral extension of the pleural suture g, prolonged 

 downward into the coxal region. The anterior region vc has been 

 termed the veracoxa (Crampton, 1914) or coxa genuina (Walton, 

 1900) and the posterior region may be termed the merocoxa, or 

 simply the meron (Walton, 1900). 



In the upper region of the veracoxa vc, there frequently occurs 

 a narrow marginal sclerite cm (Figs. 2, 3, 8, 10, etc.). In the 

 Trichoptera (Fig. 6) the region cm has been mistaken for the 

 trochantin; but the true trochantin is contained in the compound 

 sclerite ptn, which articulates with the coxa. The region cm is 

 usually small and unimportant. 



The veracoxa vc, or anterior subdivision of the coxa, may become 

 immovably united with the lower portion of the pleural plate, as in 

 certain Diptera (Fig. 11). Under these conditions, the loss of move- 

 ment in the coxa is usually compensated by the breaking off of 

 small movable plates called "coxites" (Fig. 11, cxi). The largest 

 "coxite" frequently bears a spine-like process the coxal spine, as 

 shown in Fig. 11. 



From its close connection with the epimeron in higher insects, 

 such as the Diptera, Lepidoptera, and Trichoptera, the meron me 

 (of all figures), or posterior subdivision of the coxa, has been regarded 

 by some investigators as a detached portion of the epimeron, which 

 has become adherent to the coxa. This derivation of the meron, 

 however, merely reverses the true evolutionary sequence, for in the 

 lower pterygote insects, such as the Blattoidea (Fig. 2), the meron 

 is clearly a portion of the coxa, and the suture which demarks it 

 from the remainder of the coxa is but incompletely developed in 

 these insects. In the Isoptera (Fig. 3) the meron is distinctly 

 demarked from the remainder of the coxa; but it is still clearly a 

 portion of the coxa, and is widely separated from the epimeron. It 

 is only in the higher insects that the meron becomes smaller, and 

 migrates upward toward the lower portion of the epimeron, as shown 

 in Figs. 5, 13 and 14. On this account, it is far more reasonable 

 to suppose that the meron is a demarked region of the coxa, than 

 that it is a detached portion of the epimeron which has become 

 adherent to the coxa, and the terms veracoxa and merocoxa have 

 been applied to the two subdivisions of the coxa, in order to empha- 

 size the fact that both are merely portions of the coxa itself. 



