anterior region, the divisions of the subcostal being less numerous than they are in the front wing. In the moths possessing a jugum the two wings differ but little from one {317}another, and it is probable that they function almost as four separate wings instead of as two pairs. WING-NERVURES.—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 phylogeny 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 completely 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, 1_a_, and B, 1_b_). This important condition has not yet been adequately discussed. {318}[Illustration: Fig. 161.—Wing-nervuration of Lepidoptera. I, Diagram of moths' wings (after Hampson); II, of a butterfly's wings (_Morpho menelaus_ ♂, after Staudinger and Schatz). A, front, B, hind wing. I.—_c_, costal; _sc_, subcostal; _m_, median; 1_a_, 1_b_, 1_c_, internal nervures; _f_, frenulum; 2, 3, 4, branches of median nervure; 5, lower radial; 6, upper radial; 7-11, divisions of the subcostal; 12, termination of costal; _c_, cell; _d_, discocellular nervure. II.—C, costal; SC, subcostal; M, median; SM and SN, submedian nervures; 1A, inner-margin nervure; UR, lower radial; OR, upper radial; SC^1 to SC^5, divisions of subcostal; M^1 to M^3, divisions of median nervure; C, cell; DC, discocellulars.]