EXTERNAL ANATOMY OF INSECTS. 571 



in the ample scutellum ; but if you remove this with care, 

 you will find under it their representatives, its lower sur- 

 face being hollowed out to receive them. The postdor- 

 solum appears in these as a transverse obtusangular band ; 

 in the Nepidte, Notonectidce, &c. the three parts of the 

 metaihorax seem united into a single plate, emerging 

 laterally from under the scutellum below the frcemim ; in 

 which, however, some traces of a distinction between 

 them may be discovered. In the Homopterous section 

 the Fulgoridce exhibit these pieces very distinctly, cover- 

 ed only at the base by the mesothorax : but in Tettigonia 

 they are not so easily detected ; they exist however as a 

 narrow strip or band, almost concealed by that part. 

 As to the Lepidoptera Order, in Pieris Brassicce at least, 

 the postdorsolum is represented by a pair of nearly equi- 

 lateral triangles whose vertexes meet in the centre of the 

 metathorax, and between which and the scutellum is a 

 deep cavity; but in Macroglossum Stellatarum and La- 

 siocampa Quercus, there appears to be also a central 

 transverse piece between them. In the Neuroptera there 

 is no material or striking difference between the parts of 

 the mesothorax and metathorax a . In the Hymenoptera 

 more variety occurs in this part. In the saw-flies, &c. 

 (Tenthredo L.) the postdorsolum is a transverse piece 

 covered by the scutellum; in the Ichneumonidce it is 

 smaller, but not covered ; in the Vespidce it is apparent, 

 transverse, and with the postscutellum obtusangular b ; in 

 Apis it is overhung by the scutellum. The Diptera exhibit 

 some variations in this part. In Tipula it consists of 

 three pieces placed transversely, the central one qua- 



■< Plate IX. Fig. 7- I. b Ibid. Fig 11. t' . 



