No. 1774. THORAX OF HYMEN0PTERA—SN0DGRA88. 83 



Megarhyssa lunator, with the veins named according to the Cresson 

 nomenclature, while figure 75 shows the same wing of Sirex Jlavicornis 

 (74) named by this system as modified to suit the Siricoidea and 

 Tenthredinoidea by Mr. S. A. Rohwer, of the United States Bureau of 

 Entomology. Figure 77 is the front wing of Leucospis ajfinis, and 

 the names applied to the rudiments of its veins are those in use by 

 students of the Chalcidoidea. 



The base of the Hymenopteran wing shows an increasing tendency, 

 as the higher families are approached, toward a condensation of the 

 bases of the first five veins. A very generalized wing base is found 

 in the Pamphiliid, Itycorsia discolor (64). The costal vein (C) con- 

 sists basally of two little chitinous pieces ( O and (J) . The subcosta (Sc) 

 is well developed, and articulates with the first axillary sclerite (lAx) 

 by a large and contorted base (Sc). The radius (R) is continuous 

 at its base with the second axillary (2 Ax). The media is not an 

 independent vein basally in the wing of any Hymenopteran and, by 

 the Comstock-Needham scheme of venation, it is supposed to be 

 fused with the radius, forming a compound vein (R + M), which is 

 the principal anterior vein of the wing (74). Nevertheless the little 

 median plate (to) of the wing base is generally present with which 

 both the media and the cubitus are associated in the wings of more 

 generalized insects (see fig. 8). The cubitus (Cu) is likewise com- 

 bined with the base of the radius. Consequently the next two veins 

 that enter into the base of the wing are anals. They may be known 

 as such, furthermore, by their association with the third axillary 

 {3 Ax). Since an apparent branch (74, 3 A) of the first anal is regarded 

 at the true second anal, the second one at the base of the wing is 

 called the third anal (3 A). 



The front wing of Sirex jlavicornis (65) shows a few structural 

 departures from that of Itycorsia. There is only one basal piece of 

 the costa (CO, and the enlarged base of the subcosta {Sc), articulat- 

 ing with the first axillary {lAx), is separated from the shaft of the 

 subcostal vein. These differences are more pronounced in Tremex 

 columha (66), one of the Siricidae. The shaft of the subcosta is not 

 present as a vein, though its site is marked by a short branching 

 trachea (Sc). The basal part (Sc), however, is very large and con- 

 spicuous. In Megarhyssa lunator (67), an Ichneumonid, there are 

 no traces of the subcostal shaft, but its basal part (Sc) is present and 

 articulates with the first axillary (lAx). In Pepsis (69), one of the 

 CeropalidsB (Pompilidee) , the base of the subcosta (Sc) forms a large 

 mass at the humeral angle of the wing, with which is fused the basal 

 part of the radius (R). This is evident from the articulation with 

 both the first (lAx) and the second axillary (2 Ax). Finally, in the 

 Chalcid, Leucospis (68), and in the honey bee, Apis (70), the basal 

 remnant of the subcosta (Sc) forms a large and conspicuous scale- 

 like plate on the humeral angle of the wing base. It looks like a 



