Insect wings are thought to have evolved from a gill-like thoracic segment present in early insects. Their essential material is a thin membrane covered with hair-like projections and supported by blood-filled veins. The leading edge of the wing is much stronger and stiffer than other regions of the wing, which are more elastic and capable of twisting. The areas between the veins arch up, curve down, angle and bend in a multiplicity of architectures.