WING,S OF THE TENTHREDINOIDEA—MAvdlLLlVRA Y. 619 



C^Il^3I 



of the radio-medial cross-vein, the entire vein appearing- as a trans- 

 verse vein comparable to the free part of Rr,. In J/ae/'ocep/rus mtyrus 

 (fig. 20. a) there is a further modification of the condition found in 

 Meqalodontes; the cells 1st R, and R are about eipial in length, so that 

 the vein forming their outer ends, which extends from the posterior end 

 of the radial cross-vein to the posterior end of the radio-medial cross- 

 vein, is but little longer than the free part of R-, and is only slightly 

 angulate. The fact should not be lost sight of that this vein is a com- 

 posite one, being made up of the radio-medial cross-vein and a part of 

 the radial sector. In this 

 wing the cell 2d Rj + Rg is 

 much longer, and the incli- 

 nation of the radial cross- 

 A'ein, together with the 

 course of the vein forming 

 the apices of the cells R 

 and 1st Rj, emphasizes the 

 fact still more strongly 

 that it might be the base 

 of Rj instead of the radial 

 cross-vein. That part of 

 the radial sector extending 

 from the base of the stig- 

 ma to the anterior end of 

 the radio-medial cross- vein 

 in this wing extends almost 

 longitudinally. In JanuH 

 cynoshufl (tig. 20, />), the 

 base of that part of the vein 

 just described has faded 

 out for a short distance 

 near the stigma, while in 

 Ja?/u-s ahh\'vi((tu>< (fig. 20, 

 c) the base of this vein has 

 faded out for over half its 

 length. If the remainder of the basal part of the radial sector should 



Fig. 20.— The switching of the base op the radial sector. 

 o, Macrocephus satyrus; b, Janus cynosbati; c, .Tanus 

 ABBREVIATUS: d, Oryssus abietinus; e, Pelop^eus cemen- 

 tarius; /, Apis mellifica. 



atrophy up to the point where it is joined to the anterior end of the 

 radio-medial cross-vein, and if it were not for the successive stages just 

 described, then the radial sector would be considered as arising from the 

 middle of the stigma and the entire first transverse vein, as a cross-vein. 

 This is exactly the interpretation that has been given to these veins 

 throughout the higher Hymenoptera, where this very condition exists. 

 The same condition is found in the Tenthredinoidea in the genus Oryssus 

 (fig. 20, r7), but this genus is not so interesting in this connection, 

 because the first transverse vein, i. e., the radio-medial cross-vein plus 



