164 Mr. W. S. MacLeay on the Anatomy of the 



4. The postscutellum of the metathorax corresponds with tlie meta- 

 phragma of Kirby. 



The above four pieces form the tercjum. 



The eight inferior or pectoral pieces of the metathorax are, as in the 

 mesothorax, the vietasternum, the postfurca, two episterna, two epi- 

 mera, and two paraptera, the six last being lateral and the paraptera very 

 rarely developed, and often so placed as to appear to belong to the ter^m. 



1. The metasternum of Aiidouin is very different from that of Kirby, 

 the latter being a most heterogeneous composition,* not only often com- 

 prising the true metasternum, episterna, and epimera, but sometimes 

 even confounding all these with the trochanter and coxas of the posterior 

 legs. What this gentleman calls the bifid mucro of the metathorax in 

 Dytiscus, is in reality the termination of the two coxae. The true meta- 

 sternum therefore must be studied in the beautiful figures of Audouin, as 

 well as the episterna, epimera, and paraptera where they exist. 



2. The postfurca has been described by me under one of its most 

 remarkable forms, that of the letter Y, and has been figured by Mr. Kirby 

 pi. 22,fig. 5,bt.bt. bf. 



3. The episterna of the metathorax, which possibly are what Kirby 

 cdXhparapleurce : 



4. The epimera ; 



5. And the paraptera : all hold situations in the metathorax analogous 

 to those of the pieces so named in the pectus of the mesothorax. In some 

 orders, however, the paraptera are so situated as to appear to belong to the 

 tergum. 



Hence we observe that the thorax of an insect, when greatly developed, 

 is composed of thirty-four pieces, ten to the prothorax, and twelve to the 

 mesothorax and metathorax respectively. Or, if we reckon the four pieces 

 of the tergum, with the sternum and furca of the pectus, to be each divisi- 

 ble into two by the middle longitudinal suture, as in fact they are, the 

 thorax is composed of fifty-two pieces ! So complex is the organization 

 of the thorax in vnnged insects. This, however, I say, is a great deve- 



* Mesostethium seems, with Mr. Kirby, to be sometimes the name given to 

 the episterna and sometimes to part of the metasternum. 



