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



M. Audouin has already most admirably explained the construction of 

 the thorax in Coleoptera in his dissections of Dytiscus. Let us therefore, 

 I repeat, take a Polistes. It will be easily comprehended from what I 

 have said that the tergum of the prothorax will be found exceedingly 

 diminished, and tlie tergum of the mesothorax, being so much developed, 

 must present all the four pieces of which it ought to consist. 



1. Of the Tergum of the Prothorax. 



In Polistes we observe the prcBScutum and scutum to be evanescent ; 

 the latter being represented only by a ligamentous membrane.* The 

 prsescutum possibly is the evanescent portion that passes into the head 

 and forms its upper junction with the thorax. 



The scutelhm, called collare f by Kirby, is considerably developed, 

 offering a vestige behind of the postscutellum. J The scutellum may be 

 separated with ease, as in most other Hymenopterous insects from the 

 mesothorax; but as these insects are essentially fliers, this piece of the 

 prothorax is employed to add strength to the mesothorax in its support of 

 the upper wings. In Ants therefore, and other Hymenoptera essentially 

 walkers, it comes readily enough off with the fore feet, as it should do. 



the Polistes Billardieri of his " Systema Piezatorum." However this may be, I 

 will describe the thorax of my insect according to the nomenclature here pro- 

 posed. 



Prothorax scutello flavo postice emarginato, lobis mesothoracis scutum 

 amplectentibus, lateribus deflexis subtriangularibus ; pectoris flavi sterno pos- 

 tice obscuro, antic6 marginibus lateralibus ferrugineis. 



Mesothorax scute subpentagono ferrugineo, scutelloque parallelogramico 

 flavo, sterno ferrugineo margine utrinque flavo, episternis epimeris parapte- 

 visque flavis. 



Metathobax prsBSCuto subsemicirculari flavo, scutelli striati flavi margine 

 anteriori canalique longitudinali ferrugineis, postscutello parapterisque flavis, 

 episternis metasternoque ferrugineis, epimeris flavis ad juncturam metasterni 

 ferrugineis. 



The whole length of the Insect is nearly § of an inch, and of the thorax 

 alone |. 



The above mode of describing the Thorax appears absolutely necessary when 

 species approach very near each other in their colouring and marks, as Wasps, &c. 



• Fig. 2 and fig. 3, A. B. f Fi?- 2 and fig. 3, C. t Fi?- 2, D, 



