NO. 1438. WINGS OF THE TENTHREDINOIDEA—MacGILLIVRAY. 583 



Tar)i!(>i>tery.i' (lij^-. 30), the anastomosis is for almost the entire length 

 of Sc. resulting- in a condition similar to that found in the generalized 

 Tenthredinoidea. 



IV.— A STUDY OF THE WING AREAS. 



As alread}' indicated, the wings of insects maj^ be divided into six 

 well-marked areas, an area for each of the principal veins. It is true 

 that these areas are closely interlocked in the Tenthredinoidea, but 

 this seems the most logical way of approaching the subject. An 

 attempt will 1)0 made here to describe the most important moditications 

 found in the wings of existing genera. 



1. THE FRONT WINGS. 



In all insects where the wings of a side are closely fastened together 

 for unison in flight, there is a great ditierence in the amount of reduc- 

 tion found in the two wings. It is a well-established fact that that 

 animal whose wings approximate most nearW a triangle in outline is 

 the most efficient flyer. For this reason it is apparent that when the 

 wings are of this type, as in the order llymenoptei'a, the hind wings 

 are always the ones to undergo the greater amount of reduction, and 

 consequently it has been found necessary to discuss the areas of the 

 two wings separately. 



THE COSTAL AREA. 



(Josta is a simple straight vein of the same width throughout in 

 the Lydida? (tigs. 36-48), Xyelid* (figs. 31-35), and Megalodontidas 

 (tig. 92). In most genera, ^sDolerm^i^g. 49), Pteronus {^g. 68), Blen- 

 nocanipa (fig. 72), and Eriocatnpa (tig. 47), it is decidedly thickened at 

 apex, spatulate in outline, while in the Cimbicinte (tigs. 59-60), it is 

 thickened throughout its entire length and lies adjacent to Sc + R -[- M, 

 practically squeezing out the costal and subcostal cells. 



A peculiar condition found in most of the Tenthredinoidea, though 

 not occurring outside this superfamily, so far as I have been able to 

 observe, is a hinge-like thinning out of the margin of the wing at the 

 base of the stigma. It is present in all the genera except the large- 

 bodied, active species of the family Siricidte (tigs. 86-91), and the 

 subfamilies Cimlticiua? (tigs. 59-60) and Pterygopherinas (tig. 81). It 

 represents the space on the margin of the wing between the apex of 

 the costa and the point where the second branch of subcosta joins the 

 margin. In those forms where this structure is wanting it has been 

 chitiuized secondarily, and even here its position can often be detected 

 because the band of chitin closing the space is not so broad as it is on 

 either side of it. 



The humeral cross vein, situated at the base of the wing between 

 costa and subcosta, is one of the most constant of the cross veins found 



