84 PARTIAL OR1SMOLOGY. 



the thorax (PL XIV. No. 1, f. 2, H); there remains only a small space 

 below for the passage of the intestines, the organs of the nervous and 

 respiratory systems, and of the vessels, &c. In all insects with a 

 pedunculated abdomen (abdomine petiolate), this partition is exposed, 

 and thus forms the covering of the truncated posterior portion of the 

 metathoracic segment; it even seems to distend itself towards the 

 superior surface, and to terminate only at the above indicated furrow 

 of the metathorax, whereby this becomes a positive suture (PL XII. 

 No. 2, f. 1 and 2, Scolia and other Hymenoptera). 



Directly opposite to the metanotum, and precisely in the centre of 

 the under surface, we find the METASTERNUM (PL IX., &c. G, G) ; 

 likewise very generally a quadrate, corneous plate, but which more 

 rarely takes the shape of a triangle, hexagon or octagon (Hisler, 

 PI. IX. No. 3, f. 12, G), and which helps to form anteriorly the aceta- 

 bula of the intermediate legs, and, posteriorly, those of the posterior 

 legs. It is sometimes perfectly flat, sometimes slightly convex, and 

 sometimes distinctly ridged, and occasionally prolonged posteriorly into 

 a point (Xiphus metasterni) ; arid when thus, it projects over the 

 abdomen (Hydrophilus). It differs considerably in extent in Qryctes 

 (PI. X. No. 2, f. 4, G) and Cetonia (the same, No. 1, f. 2, G) ; it 

 occupies nearly the whole pectus ; sometimes, as in Hister (PL IX. 

 No. 3, f. 12, G), only the centre ; sometimes it is compressed into 

 a comparatively small compass by the coxce of the posterior legs ; it 

 is thus formed in Dyticus (PL IX. No. 2, f. 8, G). In many Coleop- 

 tera, for example, in the Lamellicornia, the meso-and meta-sternum are 

 so closely united, that it requires violence to effect a separation. In 

 others (for example, Buprestis, PL IX. No. 3, f. 5, G), the metasternum 

 consists of two halves, which are separated by a central longitudinal 

 suture, which internally forms a ridge. 



The construction in the other orders differs materially from this 

 description of it in the beetles ; but in the Orlhoplera very slightly. 

 In these, likewise, the metasternum is a clearly distinguishable, but 

 undivided plate, placed between the acetabula of the four posterior 

 legs (PL XI. No. 2, f. 5, G). In the apterous genera, we do not 

 observe the meso- and meta-sternum to be divided into several pieces, 

 and they adhere tolerably closely to the original annular form of the 

 segments (see PI. XIII. No. 1 and 2, the thorax of the female Tengyra 

 and Myrmosa). In the Uymenoptera, the construction of the meta- 



