164 Mr. W. S. MacLeay on the Anatomy of the 
4, The postscutellum of the metathorax corresponds with the meta- 
phragma of Kirby. 
The above four pieces form the te7zqum. 
The eight inferior or pectoral pieces of the metathorax are, as in the 
mesothorax, the metasternum, 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 tergum. 
1. The metasternum of Audouin 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 cox of the posterior 
legs. What this gentleman calls the bifid mucro of the metathorax in 
Dytiscus, is in reality the termination of the two coxe. 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 
pl. 22, fig. 5, bt. bf. bt. 
3. The episterna of the metathorax, which possibly are what Kirby 
calls parapleure : 
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 winged 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. 
