INTRODUCTION. VU 



a dorsal plate, the metanotum (fig. 6, h^ n^ ; fig. 7, g, 7t\ A^), the 

 anterior portion of which is called the postscutellum ; side pieces, 

 episternum (fig. 6, I) and ejiimeroii (fig. 6, m), the two together 

 forming the metapleuron ; and the metasternum (tig. 8, /, /). 



In all the higher Hymenoptera. as noted above, the basal seg- 

 ment of the abdomen is closely amalgamated with the metathorax 

 (fig. 6, ?i, & fig. 7, A). This segment has been varionsly called 

 "Latreille's segment," the "propodeum," or the "median segment." 



Throughout this work I have preferred to use the term "median 

 segment 'as being most generally known. The median segment has 

 very often short oblique lateral slits or grooves with their anterior 

 edge raised and prominent : these slits or grooves are the so-called 

 " false stigmata '' (fig. l,j, j). The ventral plate of the median seg- 

 ment (fig. 8, h) can generally be made out with but little difficulty. 

 The sculpture of the thorax and of the median segment is largely 

 used in the discrimination of the species. 



The appendages of the thorax are the legs and the wings. The 

 legs, as in aU insects, are six in number, attached to the underside 

 of the thorax by their basal joints, the coxce (fig. 9, a) : the fore 

 legs are articulated to the prothorax, the intermediate pair to the 

 mesothorax, and the posterior to the metathorax. Below the 

 coxae are the trockanters (fig. 9, h) : these may be simple, in one 

 piece, as in the bulk of the Aculeata, or in two with an articula- 

 tion between, as in most of the Parasitica. Articulated to the 

 trochanters below are the femora (fig. 9, c) ; below these the tibice 

 (fig. 9, d), and below the tibiae the tarsi (fig. 9,/). The tarsus in 

 Hymenoptera is 5-jointed, with very few exceptions : the basal 

 joint (fig. 9, g) or metatarsus is usually the longest, the apical 

 joint (fig. 9, I) is invariably provided with two claws (fig. 9, m, m), 

 which may be simple, bifid, or dentate beneath. Between the 

 claws lies the pad or pidvillus, which, however, is absent in many 

 genera. 



The legs of Hymenoptera, especially the tibiae and tarsi, are as 

 a rule more or less furnished with spines, stiff hairs, or pubescence 

 of some kind, the presence or absence and disposition of which 

 afford valuable characters for the discrimination of species and 

 even of genera. 



The ivings (figs. 10 and 11) are invariably four in number, and 

 nearly always present in the imago in both sexes. The females, 

 and more rarely the males in a few forms, are apterous. Among 

 the Heterogyna, or Ants, the fully-developed females and the 

 males only are provided with wings, the neuters or workers (more 

 correctly the females with arrested development) being apterous. 

 The anterior wings are attached to the sides of the mesothorax 

 (fig. 6/, site of attachment of fore wing), and the points of junction 

 are protected and covered by little plates or shields, the tegtdoi 

 (fig. 6, c ; fig. 7, d, d). The posterior wings are borne by the 

 metathorax, and their points of junction with the thorax are 

 slightly lower in a vertical direction than those of the fore wings. 



