FIG. 227.—View looking down upon the upper (_i.e._ exposed) surface of one of the large scales situated on the veins of _Danais plexippus_, about four days before emergence: _clm_, chitinous pillars found in scales. _A_, _a_ smaller scale, _a_, _a′_, sections of the scales. _B_, leucocyte found in the larger scale.—After Mayer. ]
FIG. 228.—Scale-follicles: _A_, of a scale of _Galleria mellonella_: _r_, neck-ring. _B_, the same of _Polyommatus phlæas_. _C_, the same of a hair on inner edge of hind wing of _Lycæna alexis_ ♀.—After Spuler. ]
FIG. 229.—_A_, portion of wing of a caddis-fly (Mystacides). _B_, enlarged, showing the androconia and hair-scales. _C_, a separate androconium.—After Kellogg. ]
The “hair-scales” of the phylogenetically older Trichoptera correspond to certain scales of Lepidoptera, especially the Psychidæ (Spuler), variously called “plumules” (Deschamps), “battledore scales,” also certain minute cylindrical hairs. To these scent-scales is applied the term _androconia_. They are found, almost without exception, on the upper side of the fore wings, occurring in limited areas, such as the discal spots, or on folds of the wings. Fritz Müller has shown that they function as scent-scales, and are confined to the males. Kellogg has detected androconia-like scales on the wings of a caddis-fly, _Mystacides punctata_ (Fig. 229).
FIG. 280.—Cross-section of androconia surface on wing of _Thecla calanus_; _a_, androconia; _gl_, gland of base; _s_, ordinary scales; _w_, wing in section.—After Thomas. ]
Thomas has proved by sections of the wing of Danais, etc., that the androconia arise from glands situated in a fold of the wing (Fig. 230), and he states that the material elaborated by the local glands, and distributed upon the surface of the wing by the androconia, is that which gives to many of the Lepidoptera their characteristic odor. On comparing these “glands,” it is evident that they are groups of specialized formative cells of Semper (trichogens), which secrete an odorous fluid, issuing perhaps from extremely fine pore-canals at the ends of the androconia. They thus correspond to the glandular hairs, poison-hairs, and spines of caterpillars, the formative cells of which contain either a clear lymph or poison.