160 Mr. W.S. MacLeay on the Anatomy of the 
tolerably general rule being that the excessive developement of the ter- 
gum exerts an inverse influence on that of the pectus.* 
OF THE PROTHORAX. 
The prothorax of any insect at its maximum of developement consists 
then of the following pieces, viz. four tergal, which, when confluent, 
form what ought in all future descriptions of Coleoptera, according to the 
principles of MM. Chabrier, Audouin, and Kirby, to be no longer called 
the thorax, but the prothorax :+ and six pectoral pieces, which form by 
their connexion one piece that may in all future descriptions be called, as 
by Mr. Kirby, the antepectus. The four tergal pieces may be detected 
in certain Orthoptera; and the six pectoral pieces are the sternum, the 
antefurca, two episterna, and two epimera, the four latter being lateral 
pieces. 
1. The sternum of the prethorax is well known; it is an essential 
part, rarely if ever evanescent, and is called the prosternum by Kirby. 
2. The antefurca of Kirby, which is by Audouin called the entothorax 
of the prothorax, is also essential but internal. It is described by Kirby, 
vol. 3. p. 586. 
3. The episterna of the prothorax are two lateral pieces that are sup- 
ported by the prosternum, and which may be seen well developed in a 
Dytiscus. They, as well as the epimera, are confounded by Mr. Kirby 
with the prosternum.§ 
* Thus the pectus of the prothorax in large Locuste and Grylli is very small, 
owing to the developement of the tergum being at its maximum. 
+ The student who wishes to learn the structure of the prothorax, must refer 
to M. Audouin, the analysis given in the “ Introduction to Entomology” being 
very far from correct, 
{ The three sternums are often found to be more or less confluent with their 
respective epimera and episterna. Owing to the developement of the tergum, 
the pectus in Hymenoptera is exceedingly diminished. But were each of the 
sternums at its maximum of developement, it would also be found to consist 
of four pieces like a tergum. This is the case in Iulide, and is more or less 
apparent in other Annulosa. For instance, the pectus of the prothorax in 
Squilla has a presternum, sternum, sternellum, and poststernum. 
§ The pleure of M. Audouin, or ore of Mr. Kirby, appear to be the inflexed 
