134 



University of California PuUications. [Entomology 



Adolph's scheme of the dipterous wing includes not less than 

 twenty-two alternating convex and concave veins, which, with 

 the exception of a number of veins at the two ends of the series, 

 includes a concave and convex vein for every vein actually 

 existing in the vein of one of these insects. In Fig. 72 it is 

 shown that in a single family every one of the independents 

 has been treated in one species as convex and in another as 

 concave. According to this author, as has already been 

 explained, there is a fundamental difference between a convex 

 and a concave vein; consequently, veins that have been sup- 

 posed to be the same in two insects are actually different, if in 

 one case they are a little above the average level of the mem- 

 branes and in the other below it. If this were true, the whole 

 nomenclature of the systematist would be wrong. 



The third system was worked out by Comstock and Com- 

 stock ('95) and agrees in nearly every particular with that 

 adopted here, except in the terms used as names for the veins, 

 and in other slight differences dependent upon our different 

 conceptions of insect venation. This system does no violence 

 to the ideas of systematists, whose knowledge of the compara- 

 tive anatomy of this organ is certainly not to be despised. 



HYMENOPTERA. 



The venation of the Hymenoptera exhibits a remarkable 

 degree of uniformity. From the sawtlies at one extreme to the 



bees at the other, we find only 

 a single type of arrangement. 

 Such variation as occurs is all 

 in the nature of reductions 

 from the typical venation. 

 It is usually found associated 

 with small size, and is most 

 prevalent among the parasitic 

 wasps. 



While within the order the 

 problems of homology are rel- 

 atively easy, this is not true 

 when we attempt to compare this venation with those of other 

 groups. As none of the other higher orders approximates 

 closely in venation that of the Hymenoptera, there is ample 

 ground for difference of opinion. I am compelled to take a 



FIG. «0. Diagram illustrating the vena- 

 tion of the Tenthredinidfc. Dotted lines 

 show variable veins. 



