The butterfly has four _wings_, which are the largest and most conspicuous part of the insect. The wings consist of membranes stretched over horny tubes called veins; in the newly emerged insect the veins contain both blood and air, but the veins of the adult contain air only. The colors of the wing are due to minute _scales_ which cover the membranes in an overlapping fashion like shingles on a roof. The scales vary considerably in size and form as well as in color, and the males of some species bear specialized scales known as _androconia_, which produce odors attractive to the females. The third of the wing nearest the body is the _base_; the middle part of the wing is the _median_ or _discal_ area; the outer portion is called the _limbal_ area. The front edge is the _costal margin_; the outer edge is the _external margin_; the posterior edge is known as the _inner margin_. The angle of the outer and inner margins of the front wings is called the outer angle, and the corresponding angle of the hind wings is the inner or anal angle. The outmost tip of the front wing is called the _apex_. The fore wing has three simple veins: the _costal_, the _radial_, and the _submedian_. There are also two branching veins, the _median_ and the _subcostal_. The median vein has three branches or nervules, while the subcostal usually has four or five. The hind wing has five simple veins: the _costal_, _subcostal_, _upper radial_, _lower radial_, _submedian_, and _internal_. The costal vein in the hind wing usually has a short ascending spur called the _precostal_ vein but it is classed as a simple vein none the less. The median vein has three nervules, as in the fore wing. In both fore and hind wings, between the subcostal and median veins, there is an area called the _cell_, which is often closed or partially closed on the outer side by three _discocellular veins_, designated as upper, middle, and lower. Each of the six _legs_ is divided into five parts. The section nearest the body is the _coxa_, which is attached to the ring-like _trachanter_. Next beyond the trachanter is the _femur_, then the _tibia_, and finally the _tarsus_ or foot bearing the tarsal claws, which are used in clinging to various objects when the butterfly is at rest. In some species the fore legs are small and quite useless, a fact which is used in classification. THE ABDOMEN The _abdomen_ is composed of ten segments; the first seven bear _spiracles_ or breathing-holes (completely hidden by scales, however) and the last two segments are modified to form external sexual appendages. In the male there is a pair of _claspers_ for holding the female during copulation; in the female there is only a short and simple _ovipositor_. THE DIGESTIVE APPARATUS