Vol. 1.] WoodivortJi. — Wing Veins of Insects. 39 



character of the basal fold. The accompanying diagram 

 (Fig. 13) will show the characteristics of this form of articu- 

 lation. 



There is considerable variability in the exact structure of the 

 wing-roots, probably corresponding with peculiarities in the 

 .shape or stroke of the wing, and the same is true of the acces- 

 sory sclerites of the articular membrane. We will not attempt 

 to describe or discuss them, as they do not appear to affect 

 the venation of the wing. These two types of hinge structure 

 correspond with essential differences in venation, and, notwith- 

 standing their variability, exhibit nowhere transitional condi- 

 tions. 



Resume. — In conclusion, we may remark that there remains 

 abundant opportunity for study in the structures about the' 

 base of the wing. An examination of the structure of the 

 articulation of the wing of a dragonfly has shown many points 

 of difference from the accounts and figures of previous inves- 

 tigators. It proves also that the former ideas of the mechanism 

 of the wings must be considerably modified. Likewise, a study 

 of the articulation of the wing of a harvest fly brings out suffi- 

 cient differences from the account of Amans to disprove his 

 contention that there is no essential difference in the hinge 

 structure of different insects. That there are two distinct 

 types is further shown to depend upon differences in the prob- 

 able course of the development of the wang-roots. Finally, it 

 is pointed out that this corresponds with important differences 

 in venation. 



