Throughout the Heteroneura, with such exceptions as the deltoid group and a few others, the strigil remains very much the same, varying only in being a little broader or narrower, more flattened or more rounded, curved or straight. Between the strigil of the Heteroneura and that of the Homoneura, however, the difference is considerable, while the difference between the families of the Homoneura is as great as that between the suborders. In order to ascertain if any homologous structure was present in related orders, the Trichoptera and Mecoptera were examined. In the Trichoptera, species of the genera Rhyacophila, Psilochorema, Hydrobiosis, Hydropsyche, Polyplectropus, Triplectides, Notanatolica, Oecetis, Philanisus, Philorheithrus, Pycnocentria, Olinga, and Oeconesus; and, in the Mecoptera, Choristella, Nannachorista, Harpobittacus, Taeniochorista, Bittacus, Choristella, and Merope, have all yielded negative results, and it seems therefore reasonably certain that the tibial strigil in the Lepidoptera is peculiar to that order. The families of the Lepidoptera, as far as I have been able to examine them, will now be considered in order, and the modifications of the cleaning-apparatus described. Suborder Homoneura. Micropterygidae. Of this, the most primitive family of the Lepidoptera, I have examined Sabatinca and Micropteryx only. The strigil in these genera (fig. 1) is a simple leaf-shaped structure, lying, both transversely and longitudinally, convexly to the tibia (fig. 2). It is covered with hair on both surfaces, but that on the inner surface is longer, and directed chiefly towards the outer fissure, forming there a marginal fringe. At its attachment to the tibia the strigil is much narrowed, and connects to a circular base by means of a thin membrane which allows of free movement (fig. 3). This method of basal connection seems to point strongly to the strigil being a modified spur. Presumably, after development into a strigil, the structure moved basad or distad in sympathy with the tibial modification or other conditions as the different forms evolved. The base of the strigil is about the middle of the tibia, and its apex rather less than a quarter from the tibial apex. Except for being somewhat swollen round the base of the strigil, the tibia itself is not modified; there is not the flattening beneath, nor the formation of a groove, as occurs in the higher groups. Mnesarchaeidae. In Mnesarchaea the strigil is very much reduced, being only about four-fifths as long as the tibia is broad (fig. 4). It is clothed with scales similar to those on the tibia itself, and no hair is present. The reduction of the organ in this genus is apparently correlated with the type of antenna, this being filiform and scaled, with a few minute hairs. In Sabatinca the better-developed strigil is accompanied by submoniliform antennae which are thickly covered with hair. Hepialidae. In the Hepialidae the strigil is not homologous with the structure so far described; it is an outgrowth from the tibial wall instead of a modified spur. The Hepialidae are without tibial spurs, and it seems probable that they were never provided with the strigil as it exists in other Lepidoptera, but evolved a different organ to carry out the same function. At or near the base of and beneath the tibia there is a flap-like structure, covering the lower surface and extending usually about half-way along the segment the (fig. 5). There is no indication of a hinge at the base, the strigil passing