Vol. 1.] 



Woodivorth. — Wing Veins of Insects. 



117 



usually attached, and moves in the same way. Piece B, 

 shown in black, bends down under A when released, because 

 of the twist of the vein, which I interpret as the first posterior; 

 this crosses from A to B at about the middle of their length 

 (compare Fig. 56). The other veins that are under tension when 

 the wing is spread are the radiating veins given off at the distal 

 end of B. These elastic veins constitute the whole mechanism 

 of folding. The process is as follows: On the relaxation of the 

 muscle that pulls on the anterior marginal vein to keep the 

 wing expanded, the })iece B folds downward. The pull of the 

 elastic radiating veins folds downward the piece V, which pre- 

 viously resisted the strain when the wing was fiat, folding the 

 wing along the line 

 beginning between V 

 and A. The apical part 

 of the wing falls into 

 folds alternating in 

 direction and deter- 

 mined by the position 

 of the veins, in the 

 manner indicated in 

 Fig. 55. While this 

 folding process goes on, 

 the piece B is being 

 folded along the line between A and B into a position directly 

 beneath A, and all the rest of the wing takes its position 

 between the two (see Fig. 56). 



When the wing is completely folded, the under sides of A 

 and A' are in contact, and then follow in regular order B', C, 

 D' and so on. Likewise, counting from the body outward, we 

 find first B, then C, D, E, etc., in regular order. 



In spreading, the pull of the front margin straightens out 

 A and B, thus spilling out, as it were, downward and forward, 

 the rest of the wing, which is finally pulled into position as 

 the piece V is straightened out at the end of A. 



How this very complicated mechanism was brought about 

 is not an easy problem to solve. The common idea that we 

 have here simply the fan-like fold of the grasshopper doubled 

 twice after folding, in order that it could be better stowed away, 

 is certainly entirely wrong, as the figures and the description 

 of the process show. The place where the radiating veins at 



FIG. 5(i. Section across the miildle of a folded 

 wing of Forficula. Letters indicate areas, and cor- 

 respond with those on Fig. 55. 



