920 



INSECTA. 



eated, is an elevated scutellum. It is marked 

 n the median line by a longitudinal suture, 

 and in some genera by two others, one on each 

 side of this. In the Chrysididae, these lateral 

 markings completely divide the scutum into 

 three distinct pieces, the two outermost of 

 which are those to which Mr. Macleay has 

 given the name of parapsides, and which he 

 somewhat curiously suggests may probably be 

 a third pair of paraptera,* those of the pro- 

 thorax, pushed out of their proper place. But, 

 as remarked by Audouin,f in his notes to Mr. 

 Macleay's paper, were this the case, it would 

 indeed be a most singular displacement ; at the 

 same time we are compelled to acknowledge 

 that we hesitate to admit the explanation which 

 M. Audouin has given of the nature of these 

 pieces. He regards them as mere divisions of 

 the scutum, and not as elementary parts. If 

 this be the case, other parts that are consi- 

 dered as distinct pieces may with equal justice 

 be regarded as only occasional divisions of 

 more important ones. They seem rather to in- 

 dicate the division of the skeleton into a much 

 greater number of parts than are at present 

 recognized in it. We are led to this opinion 

 from the circumstance that these markings 

 exist more or less distinct in very many species. 

 We have found them very distinctly in the 

 dried skeleton of Bombus terrestris. The scu- 

 tellum (3 c) is of large dimensions in most of 

 the Hymenoptera, and is usually considerably 

 elevated above the level of the scutum. It is 

 in general of a triangular figure, and in many 

 species of this order, as well as in some Dip- 

 tera, is a marked character of the thorax being 

 often armed with spines. The post-scutellum 

 is not developed externally, but its position is 

 indicated by an elevated ridge, which is ex- 

 tended forwards on each side from the hinder 

 part of the scutellum very nearly to the base of 

 the anterior pair of wings, as in the Diptera 

 and Lepidoptera, and indicates the boundary of 

 the segment. It forms the meso-phragnia, and 

 as Mr. Macleay has remarked in Polities, is 

 connected with the scutum only at the sides, 

 being deficient in the middle line. The pec- 

 toral surface of this segment, the mesa-sternum, 

 is larger in Ichneumon Atropos (Jig. 390) 

 than in many other species. In form it is 

 nearly quadrate (3 g). It covers the whole 

 tinder surface of the segment, and is divided 

 fey a deep fissure into two halves. At its ante- 

 rior margin it is united by an indistinct suture 

 to a thin plate, the episternum, (3/,) that covers 

 the front of this part of the segment, and is 

 almost hidden behind the pro-thoracic legs, and 

 it has sometimes been considered as forming 

 part of that segment. Its lateral portion passes 

 upwards posteriorly to the collar of the pro- 

 thorax, and forms a process that projects be- 

 neath the anterior pair of wings, and above the 

 epimcron, (3 //,) which is the chief portion of 

 the side of this segment. At its inferior margin 

 this piece is united by an indistinct suture to 

 the sternum, at its anterior to the episternum,. 



and at its posterior it is articulated \vrtl* 

 the coxa of one of the middle pair of legs-. 



Fig. 390. 



* OP. ck, P . m 



h Aiinalcs de Sciences Naturales. 



1831. 



Lateral view of thorax of Ichneumon Atropos. 



2 g, episternum j 2 h, epimeron and scutellunj* 

 of pro-thorax ; meso-thorax ^36, scutum ; 3 c, 

 scutellum ; 4 d, frenum ; * *, stigma ; 3 h, epi- 

 meron ; 3 g, sternum ; 3 f, episternum \ 5, scu- 

 tellum ; 4 b, scutum of ineta-thorax j t> to 14,, 

 segments of the abdomen. 



The next segment, the meta-thorax, is an exceed- 

 ingly interesting portion of the body, owing tc* 

 the varied extent to which it is developed in- 

 the different Orders of Insects ; and on account 

 more particularly of the question that has been? 

 started, as to whether this portion of the thorax 

 in Hymenoptera is formed entirely by the 

 fourth segment of the larva, or whether a por- 

 tion of the fifth also enters into the composition, 

 of its posterior part, as believed by Audouir* 

 and Latreille. According t> Mr. Macleay, the 

 first piece of its dorsal surface or meta-notum y 

 the prfs-scuturn, is very distinct in Politics,. 

 while the scutum is concealed within the tho- 

 rax, being developed inwards to form a. 

 phragma, only a part of it being visible la- 

 terally,, but which, as usual, is connected with 

 the posterior pair of wings-, a circumstance that 

 invariably characterises the scutum in all in- 

 sects. In Ichneumon Atropos,. the prte-scutum 

 exists immediately behind the scutellum of the 

 meta-thorax, and covers part of the scutum? 

 (4 b,) which, although much encroached upon 

 in the median line by the developement back- 

 wards of this part and the scutellum of the 

 preceding segments,, is a distinct region on each 

 side of the meta-notum, and gives origin to the 

 posterior pair of wings. This sufficiently iden- 

 tifies the part as the proper scutum r otherwise 

 it might be mistaken for the prae-scutum of 

 Polistes, which is considerably more developed 

 than in Ichneumon Atropos. But the greater 

 part of the scutum is developed inwards, and 

 forms a deep cleft or incision, that divides the 

 segment into two parts transversely, the poste- 



