68 Annals Entomological Society of America [Vol. IX, 



In Periplaneta, Corydalis, Dictyophora, etc., a narrow, 

 heavily chitinized area is marked off by a suture along the 

 anterior margin of the coxa (Fig. 10, cm). Crampton, '09, 

 termed this region the " Coximarginal sclerite. " There is also 

 found in some insects a small sclerite with an inward projecting 

 process, which is free, absent or attached to the anterior margin 

 of the coxa, and is comparatively unimportant. 



A glance at the coxa of the meso- and metathorax of Per- 

 iplaneta will show that it is partly divided into an anterior and 

 posterior region (Fig. 3, m. vex). The posterior region will be 

 termed the meron (Walton, '00) and the anterior, the veracoxa 

 (Crampton '14). The suture which marks the divisions 

 of the coxa, is apparently a continuation of the pleural suture. 

 In Periplaneta the meron is partly fused with the coxa and 

 partly divided from it by a suture (Fig. 3, m). The meron 

 when present appears to be developed in the meso- and some- 

 times in the metathorax. I have never observed its presence 

 in the prothorax and in some Diptera it is absent in the pro- and 

 metathorax. Hence the development of the meron may 

 possibly have some connection with the development of the 

 wings. The coxa was probably originally one undivided 

 sclerite and the meron has been derived from it secondarily. 

 Where the meron does not occur, the coxa probably represents 

 a persistent primitive condition, such as frequently occurs 

 in insects. 



In some insects the meron is completely marked off from 

 the coxa by a suture (Fig. 4, m) and in many forms such as 

 Diptera, it has become drawn upward or enlarged, so that it 

 extends into the epimeral region and is often fused with the 

 epimeron (Figs. 1, and 2, m). This has led to its misinterpreta- 

 tion in the Diptera by Snodgrass, '09, and others, who have 

 considered it to be part of the sternum. The meron is sep- 

 arated from the sternum by membrane in such insects as 

 Tabanus, Tipula, etc., and the sternum can be plainly seen to 

 extend behind the meron (Fig. 11, msst). 



Snodgrass, '09, considered the meron as derived from the 

 epimeron. In the larva of Corydalis, he finds the epimeron 

 marked off into an upper and lower region. In the pupal stage 

 he finds that the lower portion of the epimeron has extended 

 behind the coxa and partly fused with it. In the adult, he 



