ORIGIN OF THE STING. 



165 



three pairs of abdominal tubercles destined to form the sting; 

 Z, rudiments of the legs ; fk, portion of the fatty body ; at, rudi 

 ments of the antenna? ; fl, imaginal disks, or rudiments of the 

 wings). No tracheae are developed in the larva, nor do any exist 

 in the imago. (Ganin thinks, that as these insects are some 

 what aquatic, the adult insects flying over the surface of the 

 water, the wings may act as respiratory organs, like gills.) It 

 lives six to seven days before pupating, and remains from ten 

 to twelve days in the pupa state. 



The origin of the sting is clearly ascertained. Ganin shows 

 that it consists 

 of three pairs of 

 tubercles, situ 

 ated respec 

 tively on the 

 seventh, eighth, 

 and ninth seg 

 ments of the ab 

 domen (Fig. 196, 

 tg). The labium 

 is not developed 

 from a pair of 

 tubercles, as is 

 usual, but at 

 once appears as 

 an unpaired, or 

 single organ. 

 The pupa state 

 lasts for five or 

 six days, and 



when the imago appears it eats its way through a small round 

 opening in the end of the skin of its host, the Agrion larva. 



The development of Ophioneurus, another egg-parasite, agrees 

 with that of Platygaster and Polynema. This egg-parasite passes 

 its early life in the eggs of Pieris brassicae, and two or three 

 live to reach the imago state, though about six eggs are depos 

 ited by the female. The eggs are oval, and not stalked. The 

 larva is at first of the form indicated by figure 197 E, and when 

 fully grown becomes of a broad oval form, the body not being 

 divided into segments. It differs from the genera already men 

 tioned, in remaining within its egg membrane, and not assuming 



ul 

 197. Development of Egg-parasites. 



