Thorax in tvinged Insects, 163 



The above eight pieces form the pectus of the mesothorax or medi- 

 pectus of Kirby. It is difficult to ascertain, from his not separating them 

 in his plates, whetlier the six last mentioned pieces, viz. the episterna, 

 epimera and paraptera, have been clearly distinguished by Kirby ; but if 

 they have been so, then perhaps the episterna of the mesothorax will be 

 the peristethia of Kirby and the epimera his scapularia. The pleurm of 

 the mesothorax, so called by Audouin, are the union of the episternum, 

 parapteron and epimeron. 



Of the Metathorax. 



The metathorax of an insect has also, when at its maximum of deve- 

 lopement, four pieces to the tergmn and eight to the pectus. 



The four superior or tergal pieces of the metathorax are, as in the 

 mesothorax, the prascutum, scutum, scittellum, and postscutellum. 



1. T\iQ prcEscutum of the metathorax, like that of the mesothorax, is 

 sometimes internal.* In Hymenoptera, however, it is a most conspi- 

 cuous piece with many insects. 



2. The scutum is sometimes divided into two parts, as in Dytiscus, 

 and sometimes connected, as in Lucanus.f 



3. The scutelhm is the next piece of the metathorax and is composed 

 of the postscutellum and postfranum of Kirby ; this naturalist having 

 mistaken the side processes of the scutellura for separate pieces % on ac- 

 count of the channel which divides them longitudinally. 



tera generally below. It is a piece which " se prolonge quelquefois inferieure- 

 " ment le long du bord ant^rieur de repisternum, ou bien, devenant libre, passe 

 " au devant de I'aile et se place meme accidentellement aii-dessus." On this 

 account M. Audouin changed its name from hypopteron to parapteron. In 

 Hymenoptera it may often be said to belong to the tergmn, and in Coleoptera to 

 the pectus. 



* See Ann. des Sciences Nat., Tom. I, tab. 8. Mr. Kirby calls this piece the 

 mesophragma when it occurs in Coleoptera; but in Hymenoptera, he calls it the 

 postdorsolum, as will be seen by comparing his figures. 



t See Int. to Ent. tab. 8. This piece in Coleoptera is Kirby's postdorsolum ; 

 in Hymenoptera he does not appear to have detected it. 



J The metapnystega of Kirby may possibly be the same as Audouin's peri- 

 trema of the Metathorax. 



l2 



