In many butterflies the fore legs are small and shortened, and of little use, and held pressed against the breast. In the Lycænidæ the fore tarsi are without claws; in Erycinidæ and Libytheidæ the fore legs of the males are shortened, but completely developed in the females, while in the Nymphalidæ the fore legs in both sexes are shortened, consisting in the males of one or two joints, the claws being absent in the females. Among moths loss of the fore tarsi is less frequent. J. B. Smith[21] notices the lack of the fore tarsi in the male of a deltoid, _Litognatha nubilifasciata_ (Fig. 113), while the hind feet of _Hepialus hectus_ are shortened. In an aphid (_Mastopoda pteridis_, Esl.) all the tarsi are reduced to a single vestigial joint (Fig. 114). [Illustration: FIG. 113.—Leg of Litognatha: _cx_, coxa; _f_, femur; _t_, tibia; _ep_, its epiphysis, and _sh_, its shield-like process. The tarsus entirely wanting.—After Smith. ] Entirely legless adult insects are rare, and the loss is clearly seen to be an adaptation due to disuse; such are the females of the Psychidæ, the females of several genera of Coccidæ (Mytilaspis, etc.), and the females of the Stylopidæ. Apodous larval insects are common, and the loss of legs is plainly seen to be a secondary adaptive feature, since there are annectant forms with one or two pairs of thoracic legs. All dipterous and siphonapterous larvæ, those of all the Hymenoptera except the saw-flies, a few lepidopterous larvæ, some coleopterous, as those of the Rhyncophora, Buprestidæ, Eucnemidæ, and other families, and many Cerambycidæ are without any legs. In _Eupsalis minuta_, belonging to the Brenthidæ, the thoracic legs are minute. The legs of larvæ end in a single claw, upon the tips of which the insect stands in walking. _c._ Locomotion (walking, climbing, and swimming) =Mechanics of walking.=—To Graber we owe the best exposition of the mechanics of walking in insects. “The first segment of the insect leg,” he says, “upon which the weight of the body rests first of all, is the coxa. Its method of articulation is very different from that of the other joints. The enarthrosis affords the most extensive play, particularly in the Hymenoptera and Diptera.”