N0.143S. WTN(,'S OF THE TENTHREDTNOTT)EA—MAfaTLLTVRAY. fill 



regards the number and arrangement of their veins and trusses is 

 contirmed by field observations that prove that this insect not onl}^ has 

 wings that are poorlv fitted for a rapid flight, but that in fact it is an 

 extremely poor flyer. 



If now the different groups representing families and subfamilies 

 be examined, l>eginning with the more generalized, it will be found 

 as we proceed from generalized to specialized that there is a gradual 

 approximation to the type described for Bhinxx'itmjxi^ while in otlun- 

 grouj)s more specialized than Blenn(>C(inip<( that the conditions are 

 even uiore perfect than in this genus. These modifications are read- 

 ily traceable in the change in position of the radial cross-vein, its 

 posterior end swinging toward the apex of the wing and forming one 

 side of a truss behind the stigma; the moving of the medio-cubital 

 cross-vein from a position between media and cul)itus, where it is 

 only of secondary importance in transmitting stress, to a position 

 between radius and cubitus, where it is of primary importance; the 

 migration of M^+Cui until it is practically in line with the medio- 

 cu})ital cross-vein; the shortening of the radio-medial cross- vein and 

 the free parts of R^, R^, and R.,, in this way greatly strengthening the 

 area lying between the most important areas of trusses, those of the 

 stigma and those of cell Mj. The reduction of the anal cells of the 

 front wings, the second anal cell ))eing of only secoiKUuy imi)ortance, 

 the l)ase of the third anal vein is gradually atrophied, and the wing 

 memln-ane occupied by it reduced until the petiolate type of cell is 

 obtained, which is gradually modified fui-ther l)y coalescence, and the 

 furthcn- reduction of the wing membrane until the condition existing 

 in the higher H3'menoptera is reached by certain subfamilies of the 

 family Tenthredinidce. The migration of the apex of- R^ away from 

 the margin of the wing, forming an appendiculate cell, to a })osition 

 opposite the apex of the wing. Those genera in which this type of 

 cell has been developed have their wings greatly elongated, and the 

 migration of R^ is to stiffen this increased sail area. 



The migration of the transverse parts of the veins, due to an effort 

 to form more efficient trusses, results in a marked modification of the 

 position of these veins, and one of frequent occurrence. Where there 

 is a secondary change in the position of veins, it can generallv be told 

 by a comparison with the generalized forms. This is shown in the 

 wings of Pachylota (fig. 77), L(tl>!(](ir(j<' (Hg. 7.S), Lolxxyi'ds (fig. S2), 

 and Petujn (fig. 84), where the transverse part of M, has migrated 

 aU)ng R., + Mj +a on one side and along the medial cross-vein on the 

 other. 



When the wings of the Lydida- (figs. 36-43) or Xyelida^ (tigs. 31-35) 

 are compared with those of Blernux-ajiijxi^ one of the most noticeable 

 features is the great mimber of veins. The greater efficiency of the 

 truss system of the wiugs of Blennovatitjxi over that of the man}" 



