OVIPOSITORS AND STINGS. 3 71 



In some larvae (MyrmecoZeo, Dytiscus) 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 

 Hymenojrtera, of Myrmecoleo, and of the Pupipara. The 

 salivary glands secrete the silken material in which the larvse 

 of the Lepidoptera invest themselves ; while, in Myrmecoleo 

 and the Hemerobidoe, 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, 

 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 Diptera 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 l'armure genitale femelle des Insectes." (" Annales des 

 Sciences Naturelles," 1849-1853.) 



