EXTERNAL ANATOMY OF INSECTS. 707 



hind in a piece resembling in some measure the scutellum 

 of the Stratyomidcs and similarly armed with a pair of 

 spines a : in E. aculeata the sides of the abdomen, un- 

 der the plate, have a number of longitudinal folds like 

 those of Phrynus. In Cryptocerus, a genus of ants pecu- 

 liar to South America, the Jirst segment, not reckoning 

 the pedicle, forms almost the whole back of the abdomen, 

 and the three last are so minute as scarcely to be distin- 

 guishable. Nothing very remarkable is exhibited by the 

 other segments, except that in Trichius the penultimate 

 is the largest; in some 8taphylinid.ee (S. splendens) and 

 Brachini ( B. melanocephalus) it is emarginate, and in the 

 former tribe also often terminating in a white membrane. 

 The dorsal segment most worthy of notice is the last, which 

 is called the podex ; for though in general it is a minute 

 piece, often retracted within the abdomen and invisible, 

 as in many Diptera, yet sometimes it is the most con- 

 spicuous of the dorsal segments. It is most commonly 

 triangular, and usually deflexed and forming an angle 

 with a horizontal line; but in Clytra, Cfilamys, and 

 Oryctes, it is inflexed ; in many Lamellicorns it is nearly 

 vertical. In Tettigonia F., many other Homopterous 

 Hemiptera, and some Hymenoptera (Cimbex), its sides 

 turn down and become ventral ; on its lower side it has 

 in these a longitudinal cavity which receives the oviposi- 

 tor in repose 5 . In many other insects it unites with the 

 last ventral segment, the hypopygium, to form a tube 

 for that organ, as you will find in Callidiun violaceum , 

 many Mnscida?, and Thelyphonus. As to its termination 

 the podex is sometimes bifid, Blatta; bipartite, Ranatra ) 



a Plate XV. Fig. 10. h Reaum. v. /. xvii./ 14. a. a. 



c Linn. Trans, v. t. xii./. 15. 



2 z 2 



