. THE ABDOMEN. 15 



thorax, but may be shorter. It is never quite cylin- 

 drical, being usually somewhat flattened above and 

 beneath. With Selandria it is ovoid, is longer and 

 more rounded with the Tenthredina, and much flat- 

 tended with Lyda. With the Tenthredinaitbvlgea out 

 in the middle : Cimbey has the dorsal surface some- 

 what arched, curved down towards the apex, and the 

 belly flattened with the sides sharp. A few forms 

 have the apical segments much contracted. On the 

 apex of the eighth (or ninth, counting the fourth 

 segment as abdominal) segment (which has sometimes 

 no dorsal arc) are two unjointed projecting organs, 

 called cf'Tcl. They are seldom very conspicuous, but 

 with Cryptocampus, &c., they are very prominent. 

 What may be their use is still an unsettled ques- 

 tion, but probably they act" in some way as tactile 

 organs. 



The separation of the abdomen from the above-men- 

 tioned fourth thoracic segment is usually marked by 

 a transverse incision, covered with a white membrane, 

 which with Cimbex and many other genera is very 

 conspicuous, and is called the blotch (nuditas}. The 

 abdomen thus, according to the above view, consists 

 of eight segments. Of course, if the fourth is to be 

 regarded as abdominal, the number would be nine, 

 and certainly the fourth has every appearance of 

 forming part of the abdomen, if we neglect other 

 considerations.* 



While, as has been said, the last segment is not at 

 all, or but slightly, developed above, below it forms 

 two oval or oblong plates, cleft in the middle (PI. X, fig. 

 5 1, 3, PI. X, fig. 4, 8), which are called the hypopygial 

 wlces. They are seldom of great size, rarely occupying 

 one fourth of the length of the abdomen, except with 

 those species, e.g. Nematus luteus, which oviposit in 

 twigs, and consequently require a long and strongly- 



* As a matter of convenience, and to facilitate comparison with 

 Continental works, in the descriptions I have counted the number of 

 segments as nine. 



