CHAPTER XXIII 



HYMENOPTERA PETIOLATA PARASITIC HYMENOPTERA CYXIPIDAE 



OR GALL - FLIES PROCTOTRYPID AE CHALCIDIDAE ICHNEU- 



MONIDAE BRACONIDAE - STEPHANIDAE MEGALYRIDAE 



EVANIIDAE PELECINIDAE TRIGONALIDAE. 



WE now pass to the consideration of the Hymenoptera of the 

 sub-Order Petiolata, or Apocrita, as they are styled by Brauer. 

 We should make use of the term Petioliventres, for it contrasts 

 naturally by its termination with Sessiliventres, were it not that 

 the word is so uncouth that we think it better to adopt the 

 shorter and more euphonious expression, Petiolata. 



The members of this sub-Order, without exception, have the 

 hind body connected with the thorax by means of a deep con- 

 striction, so that the base of the abdomen (Fig. 336, B, &) is 

 very narrow ; the articulation between the two parts is effected 

 by means of a complex joint allowing great play, and facilitating 

 the operations of boring and. stinging, processes that are of 

 extreme importance in the economy of the great majority of the 

 species. The petiole is sometimes extremely short, but it may 

 be so long that it appears like a stalk, at whose extremity is 

 borne the remaining part of the abdomen (Fig. 369). When 

 the petiole is very short the abdomen reposes close to the back 

 of the thorax (Fig. 331, C), and in this case the abdomen is 

 usually described as sessile ; while, when it is evidently stalked, 

 it is said to be petiolate. These terms are, however, unsuitable, 

 as the words sessile and petiolate should be reserved for the 

 conditions characteristic of the two sub -Orders. We shall 

 therefore use the terms pseudo-sessile and pedicellate for the 

 two conditions of the Petiolata. 



The Hymenoptera Petiolata comprises an enormous majority 



