172 Mr. W.S. MacLeay on the Anatomy of the 
developed, and preserves much the same form that it has in many Coleop- 
tera. In Polistes the form somewhat resembles two quadrants, the radii 
of which are joined together at their respective curves. The external 
margin of this piece may possibly be what Mr. Kirby callsthe postfrenum 
of Hymenoptera,* and its internal developement may be perhaps his 
mesophragma ; although, to judge from his mesophragma as it exists in 
Hymenoptera, he does not seem to have viewed it internally, where he 
would have found the scutum to be a very essential piece. 
3. The scwtellum of the metathorax comes next after the scutum, to 
the anterior margin of which it is joined, so as to present the external ap- 
pearance of immediately following the prescutum, while thescutum takes 
its vertical direction as aseptum. In Hymenoptera this in general is ob- 
liquely striated, and a very large and conspicuous piece.t As in Coleop- 
tera, it often consists of two large convex pannels,+ joined together by a 
channel, which however in this orderis more or less evanescent. This 
channel of connexion Mr. Kirby does not notice in his figures of Hymen- 
optera, although, according to his nomenclature, and taking a Coleopte- 
rous insect for type, it ought to be his postscutellum. His postscutellum 
in Hymenoptera, however, is little more than the central posterior point 
of the prescutum of the metathorax, that is, of his postdorsolum.§ 
4. The postscutellum of the metathorax in our insect is elevated, sub- 
triangular with the corners rounded off, and having in the middle an ele- 
vation of a horse-shoe form, in which are three apertures, the central one 
being a longitudinal slit, called by Kirby the trochlea,|| and. throuzh 
* What this author calls the postfrenum in Coleoptera belongs to an entirely 
different piece, namely, the scutellum of the metathorax. 
+ In Polistes the metathoracic stigmata (7) are situated at the anterior ex- 
ternal angles of this piece, which is represented fig. 5, K. 
} The two pannels of this piece in Coleoptera are called by Mr. Kirby post- 
frena, and its connecting channel in the same order is his postscutellum. 
§ See Int, to Ent., Vol. IlI., p. 572. 
|| I have adopted this nomenclature, although my readers must feel that this 
story of the pulley depends more on Mr. Kirby’s imagination than on any thing 
in nature. Mr. Kirby seems to think that he is the first who has noticed this 
curious structure of the metathorax of a wasp. If he refers, however, to M. 
Chabrier’s excellent Memoir, Mém. du Mus., Vol. Ill., p, 53, he will find the 
