OVIPOSITORS AND STINGS. 371 



In some larvae (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 

 Hymenoptera, of Myrmecoleo, and of the Pupnpara. The 

 salivary glands secrete the silken material in which the larvae 

 of the Lepidoptera invest themselves ; while, in Myrmecoleo 

 and the JSemerobidoe, 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 (Hymenoptera, Lepidoptera, 

 JVeuroptera). 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 Dlptera the pos- 

 terior wings are represented only by short processes, the hal- 

 teres. In the Strepsiptera, 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 stings 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 sur Farmure grenitale femelle des Iusectes." (" Annales des 

 Sciences Naturelles," 1849-1853.) 



