WING-NERVURES 3 I 7 



another, and it is probable that they function almost as four 

 separate wings instead of as two pairs. 



WING-NEKVURES. The nervures or ribs of the wings are of 

 great importance in Lepidoptera, as at present they furnish the 

 chief characters for classification and for the discussions of 

 phylogeuy that are so numerous in entomological literature. 

 On looking at wings that have been deprived of their scales it 

 will be noticed (Fig. 161) that the ribs are much more numerous 

 at the outer margins than they are near the points of attachment 

 of the wings, and that there is usually but one cell (or area com- 

 pletely enclosed by ribs). This latter point is one of the chief 

 peculiarities of the Lepidopterous wing ; in Insect-wings generally 

 the number of cells in proportion to the area of the wings and to 

 the number of nervures is greater than it is in Lepidoptera, for 

 in the latter there are few or no cross-nervures. Hence there is 

 sometimes no closed cell at all on the wing (Fig. 161, II. B). 

 The maximum number of closed cells is six ; this is found in 

 some species of Micropteryx, while in Hepialus there may be 

 three or four ; but the rule is that there is only one cell in the 

 Lepidopterous wing. When the number of cells is increased 

 this is not necessarily due to an increase in the cross-nervures; and 

 in fact it is generally due to irregular forking or to the sinuous 

 form of the longitudinal nervures themselves (see wing of Castnia, 

 Fig. 162, A.). Some authorities consider that all transverse or 

 cross-veins in Lepidoptera are merely portions of longitudinal 

 veins having diverted courses. When a portion of a nervure 

 beyond the basal or primary portion serves as a common piece 

 to two forked parts external to it, it is called a stalk (Fig. 162, 

 A, e). There are cases in which the furcation takes place in the 

 opposite direction, so that a nervure is double at the base of the 

 wing (Fig. 161, I, A, la, and B, 1&). This important condition 

 has not yet been adequately discussed. 



Turning to the mode of designation of the nervures, 1 we may 



1 It is impossible for us to treat of the difficulties that exist on this point, and 

 we must refer the student to the pamphlet, "The Venation of the "Wings of 

 Insects," by Prof. Comstock, Ithaca, 1895, being a reprint, with an important 

 prefatory note, from the Elements of Insect Anatomy, by J. H. Comstock and V. L. 

 Kellogg, also to Packard's discussion of the subject in Mem. Ac. Sci. Washington, 

 vii. 1895, pp. 84-86. The method of Spuler, alluded to in these two memoirs, is 

 based on development, and, when extended, will doubtless have very valuable 

 results. See Spuler, Zeitschr. wiss. Zool. liii. 1892, p. 597. 



