708 EXTERNAL ANATOMY OF INSECTS. 



mucronate, Sirex; acuminate, Melolontha vulgaris, Tri- 

 chius hemipterus. Generally this part is flat ; but the disk 

 is elevated or gibbous in Oryctes and some other La- 

 mellicorns. In the majority of the Coleoptera Order it 

 is quite covered by the wings and elytra ; but in many of 

 the last-mentioned tribe, and sometimes the penultimate 

 segment also, it is not covered by them a . In some in- 

 sects the piece we are considering appears to consist of 

 two segments; in the male of Locusta morbillosa the 

 whole podex is rhomboidal, but it is formed by two tri- 

 angular pieces which articulate with each other; this 

 structure permits the more easy elevation of the terminal 

 one for the extrusion of the feces. 



Ventral Segments b . We are now to turn our atten- 

 tion to the ventral segments of the abdomen. The first 

 of them is what is called the epigastrium c in the table. 

 This part, according to M. Chabrier, is of considerable 

 importance to the animal in flight, as, by its pressure 

 against the trunk, not only regulating the movements of 

 the abdomen, but as, in his opinion, contributing to push 

 forward the trunk d in the descent of the animal. It is 

 remarkable only in the Coleoptera and Heteropterous 

 Hemiptera, to which my observations upon it will be 

 confined. It may be stated as usually consisting of two 

 articulations, that nearest the trunk being narrow, and in 

 the Predaceous beetles e , as also in Scutellera, Pentatoma, 



a Daldorf (Asiatic Society's Trans, vii.) has divided Geotrupes into 

 two families, one with the podex covered (G. verna/is, &c.) which he 

 calls modesti, the other with it uncovered {G. stercorarius, &c.) which 

 he calls obscceni. t> Plate VIII. E. 



c Ibid. D. d Sur ie Vot des f m ] c j Addend. 299. 



e In Dytiscus marginalis the upper side of the margin of the Hy- 

 pochondria is curiously cut into transverse corrugations. 



