6 G. C. Cbampton aud W. H. Hasey, 



sternal region, by the formation of secondarj' sutures, not present 

 in other insects, and is therefore an entirely diiferent plate from 

 the trochantin, which is frequently present in certain grasshoppers. 

 Both of the sclerites ac and sc, which occur as distinct sclerites in 

 the metathorax of the grasshopper (Fig. 16), are included in the 

 circular region per, which forms a ring above the base of the coxa, 

 in the mesothorax of this insect (Fig, 17). 



Near the base of the coxa there occurs in certain insects, a 

 small sclerite jc (Figs. 1, 19, and 22) which frequently bears an 

 internal process to which are attached certain of the muscles which 

 move the coxa. In the meso- and metathorax of the roach Peri- 

 planefa, it is situated close to the margin of the coxa, and in most 

 insects, it is indistinguishably united with the coxa. It is always 

 small and unimportant. 



The coxa. 



In the prothorax of the Plecoptera (P'ig. 21) and in the meso- 

 and metathorax of the Myrientomata (Fig. 20), the coxa ex is reduced 

 to a rather narrow ring, being broader than long in these insects. 

 In the Thysanura (Fig. 18) on the other hand, and in many winged 

 insects, the coxa is longer than broad. In certain beetles, the 

 posterior coxae are transversely elongate and extremely flat (Fig. 24) 

 and being set in the coxal cavities, they lie in the same plane with 

 the sternal region, and were frequently mistaken for a portion of 

 the sternum by certain of the earlier entomologists. 



In the meso- and metathorax of certain Thysanura, such as 

 Maclnlis (Fig. 18), the coxa bears a styliform appendage stg strongly 

 suggestive of the so-called styli of Myriopods. These styliform 

 appendages, however, bear no relation to the meron, or posterior 

 region of the coxa, presently to be described, althougli some writers 

 have sought to homologize the two. 



The coxa is not divided into an anterior and posterior sub- 

 division in the apterygote, or primitively wingless insects, nor is it 

 so divided in any of the larvae of winged insects examined by the 

 writers. Certain adult pterygote insects have also preserved the 

 primitive undivided condition in the coxae of all of the thoracic 

 segments, and in those segments which do not bear a functional 

 wing (such as the prothorax of all insects, and the mesothorax of the 

 Diptera) the coxa is always undivided. 



In the meso- and metathorax of many winged insects, the coxa 



