160 Mr. W. S. MacLeay on the Jnatomy of the 



tolerably general rule being that the excessive developement of the ter- 

 gura 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 :f 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 prothorax is well known ; it is an essential 

 part, rarely if ever evanescent, and is called the prosteriium 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 th;it 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 prosternnm.% 



* Thus the pectus of the prothorax in lar^e LocustcB a-nd Grylli is very small, 

 owing to the developement of the tergum being at its maximum. 



f 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 ft-om correct. 



J 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 lulidx, and is more or less 

 apparent in other Annulosa. For instance, the pectus of the prothorax in 

 Squilla has a presternum, sternum, sternellum, and poststermim, 



§ The pleurce of M. Audouin, or orce of Mr. Kirby, appear to be the inflexed 



