CLASSIFICATION. 



43 



Bulletins, Entomology, vol. i, no. 1, pp. 1-152), in which he deals 

 with the flight and venation of insects ; in it he has paid special 

 attention to the lines of folding, which are almost as interesting as 

 the veins themselves, and by his kind permission we are enabled to 

 give figures of the methods of folding in the case of three types of 

 wings. " The most characteristic thing," he says (I. c. p. 126), 

 " about the hind wing in this order is the manner of folding. These 

 wings exhibit a good deal of variation in this respect, but there is 

 one point in which they all agree, if the wing folds transversely at all 

 — abortive wings, or those not fully covered by the elytra, lose the 

 characteristic fold that occurs in all normal wings. This common 

 character is the dividing of the area between the two strong 

 divergent veins [called by him the primary and first posterior] into 



Fig. 21. — Venation and folding of wings of Harpalus caliginosus ; Adephagid 

 type. Dotted lines indicate lines of folding ; black areas those that are 

 reversed in folding. (After Woolworth.) 



four triangular areas by the lines of folding [the triangles are seen 

 in the figure]. Besides these there is always one and sometimes 

 two basal folds, and there are also extremely variable apical folds. 

 The method of folding is as follows: the largest white area, the 

 third coming from the margin near the base, is the only one that 

 remains uncovered. All the adjacent areas bend under it. The 

 tip of the wing beyond the triangles folds first longitudinally along 

 a slight curve, which causes the extreme tip to fold back upon the 

 more basal portion. The folding is brought about in the first type 

 of wing [fig. 21] by the approximation of the tips of the primary 

 and first posterior (radial and median) veins by their own elasticity, 

 and the extension of the wing by a pull on the anterior marginal 

 (costal and subcostal) veins by the anterior muscles. The folding 



