If a section be made of the perfect wing of a Lepidopteron, it is found that the two layers or walls of the wing are firmly held together by material irregularly arranged, in a somewhat columnar manner. The thickness of the wing is much greater where the section cuts through a nervure (Fig. 170, A). The nervures apparently differ as to the structures found in them. Spuler observed in a nervure of _Triphaena pronuba_, a body having in section a considerable diameter, that he considered to be a {330}trachea, and also a "wing-rib" and blood-cells. He remarks that even in nervures, perfectly formed as to their chitinous parts, either wing-rib or trachea or both may be absent.[194] Schäffer[195] was unable to find any tracheae in the completed wings he examined, and he states that the matrix of the tracheae and even their inner linings disappear. The wing-ribs were, however, found by him to be present (Fig. 170, A and B). [Illustration: Fig. 170.—Structure of wing of imago. A, Transverse section of basal portion of wing [of _Vanessa_?] containing a nervure; _c_, cuticle; _fr_, wing-rib; _g_, wall of nervure ("Grundmembran"); _h_, hypodermis; _p_, connecting columns: _r_, lumen of nervure; B, section of a rib; _b_, one of the chitinous projections; _str_, central rod. (After Schäffer.)] [Illustration: Fig. 171—Scales of male _Lepidoptera_. A, Scale from upper surface of _Everes comyntas_; B, from upper surface of _Pieris rapae_; C, from inner side of fold of inner margin of hind wing of _Laertias philenor_; D, one of the cover-scales from the costal androconium of _Eudamus proteus_; E, F, G, scales from androconium of _Thorybes pylades_. (After Scudder).]