OVIPOSITORS AND STINGS. 371 



In some larv.ne {Myrmecoleo, Dytisciis) there is no proper 

 median oral aperture, but canals which open on the extremi- 

 ties of the mandibles lead into the oesophagus. The alimen- 

 tary canal has no posterior opening in the larvae of many 

 Hi/menoptera., of Myrmecoleo, and of the Pupipara. The 

 salivary glands secrete the silken material in which the larvae 

 of the Lepldoptera invest themselves ; while, in Myrniecoleo 

 and the Hemerohldoi^ it is the rectum which furnishes the silk. 



The poison of the Hymenoptera is a fluid strongly im- 

 pregnated with formic acid, which is secreted by a special 

 gland and poured into a reservoir connected with the sting. 



In many winged insects both pairs of wings are developed 

 and take equal shares in flight {Hyiuerioptera^ Lepldoptera^ 

 Neuropterci). In the Coleoptera, the anterior pair are con- 

 verted into horny wing-covers (elytra)^ and the posterior pair, 

 much larger than the anterior and folded up under them when 

 the insect is at rest, subserve flight. In the Blptera the pos- 

 terior witigs are represented only by short processes, the lial- 

 teres. In the Strepslptera^ on the other hand, it is the ante- 

 rior pair of wings which abort. In all orders of winged in- 

 sects, individual cases of complete abortion of the wings oc- 

 cur either in the female alone, or in both sexes. 



The posterior abdominal somites often undergo extensive 

 modifications ; they may be small and retracted within the 

 anterior somites, or they may even become more or less com- 

 pletely abortive. In many insects, processes of the somites 

 in the genital region of the females, which answer to the go- 

 napophyses of Blatta^ are converted into organs which assist 

 in the deposition of the eggs, and are termed ovipositors. 

 The saws of the Saw-flies and the stino-s of other Hymenop- 

 tera are to be regarded as specially modified ovipositors. The 

 laborious and thoughtful investigations of Lacaze-Duthiers ^ 

 led him to the conclusion that all these organs are constructed 

 upon the same plan ; that they are developed from that so- 

 mite of the abdomen which lies immediately behind the open- 

 ing of the vulva ; that this opening is always situated be- 

 tween the eighth and the ninth somite ; and is therefore 

 separated by three somites (the ninth, tenth, and eleventh) 

 from the anus. 



According to Lacaze-Duthiers, in those insects which are 

 provided with an ovipositor, saw, or sting, the ninth somite 



1 " Recherches siir TarmuTc ijenitale femelle des Iiisectes." (" Annales des 

 Sciences Naturelles," 1840-1853.) 



