HYMENOPTERA. 603 



The Parapsides. in this order the scutum ot the mesothorax is 

 divided into three parts by two longitudinal sutures ; the lateral por- 



FIG. 732. A Chalcis-fly : i. pronotum ; 2, 2, parapsides; 3, mesal part of the scutum of 

 the mesothorax ; 4, scutellum ; 5, tegnlae. 



tions of the scutum thus separated from the mesal part (Fig. 732, 2,2) 

 are termed the parapsides (pa-rap'si-des). 



The Wing-veins. It is much more difficult to determine the 

 homologies of the wing-veins of the Hymenoptera than those of 

 either the Lepidoptera or the Diptera; for in this order the primitive 

 plan is much more obscured. The best way to learn the wing-veins 

 of the Hymenoptera is to make first a careful study of those of the 

 Diptera, and then to compare the front wing of a generalized 

 hymenopterous insect with a wing of one of the more generalized 

 Diptera ; for this purpose take the front wing of a saw-fly of the 

 genus Pamphilius (Fig. 733) and that of Tabanus (Fig. 539, p. 454). 



In Pamphilius (Pam-phil i-us), and in most other Hymenoptera 

 also, the anal furrow or vein VIII is easily recognized as a concave 

 fold, in the position indicated by the dotted line (Fig. 733, VIII). 

 Having found this, a very important landmark is established. 



Next it should be understood that the Hymenoptera belong to 

 that series of orders in which veins IV and VI are not developed ; 

 therefore the veins that lie in front of the anal furrow are veins I, II, 

 III, V, and VII. 



Vein I forms the costal border of the wing, as in the Diptera 



(Fig- 733, I). 



Vein II is usually absent in the Hymenoptera; but in Pamphilius, 

 and in a few other genera, it is well preserved (Fig. 733, II). It is 

 simple, and is usually connected with vein III by a cross-vein. 



Vein III is the most difficult of all of the veins to understand. A 

 very careful study of the problem has convinced the writer that this 

 vein is typically five-branched in this order, resembling in this re- 



