38 



University of California PuUications. [Entomology 



ing points of the primitive wing. The form of the connection 

 with the notum will be essentially different according to the 

 method followed. When the wing-root is developed from the 

 veins immediately adjacent to the bearing points, the structure 

 will admit of greater movement at right angles to the direction 

 of the stroke. The perfection of this type of articulation per- 

 mits the complete flexion of the wing and requires provision 

 for its expansion. 



The attachment of a flexiible wing usually shows three 

 strong veins, as in the insect just described and shown at the 



FIG. 13. Diagram illustrating the flexion of a wing. AM, anterior 

 margin; PM, posterior margin; P, primary vein. 



three black areas in Fig. 12. These three consist of the vein 

 I have called the primary and usually the one immediately in 

 front of or behind it, which at the base takes a position 

 directly above or below the primary, the two forming the 

 hinge for flexion, and in front of these a third vein, which is 

 broken in one or more places near the base by soft, elastic, 

 telescopic sections and is connected by a tendon to the exten- 

 sor muscle, within the thorax. Behind the hinge all the veins 

 stop short and are separated from the body by a flexible area, 

 in which there are usually developed a number of floating 

 articular sclerites very variable in shape, number, and position. 

 Their weakness and variability prove them to be of very second- 

 ary importance in flight, but they will doubtless show, when 

 more fully studied, a distinct and important relation to the 



