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 the tergum of the mesothorax, being so much developed, 
must present all the four pieces of which it ought to consist. 
1. Or tHe TERGUM OF THE PROTHORAX. 
In Polistes we observe the prescutum and scutum to be evanescent ; 
the latter being represented only by a ligamentous membrane.* The 
prescutum possibly is the evanescent portion that passes into the head 
and forms its upper junction with the thorax. 
The scutellwm, called collare + by Kirby, is considerably developed, 
offering a vestige behind of the postscutellum.t 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, 1 
will describe the thorax of my insect according to the nomenclature here pro- 
posed. 
PROTHORAX scutello flayo posticé emarginato, lobis mesothoracis scutum 
amplectentibus, lateribus deflexis subtriangularibus; pectoris flavi sterno pos- 
ticé obscuro, anticé marginibus lateralibus ferrugineis. 
MEsoTHORAX scuto subpentagono ferrugineo, scutelloque parallelogramico 
flavo, sterno ferrugineo margine utrinque flavo, episternis epimeris parapte- 
risque flavis. - 
METATHORAX prescuto 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 3, 
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. + Fig. 2and fig, 3, C. t Fig. 2, D. 
