Behind the head, the body consists of at least fifteen segments. Most of the segments bear a single pair of legs; the maxillipeds project forward from the first body segment, while the final two segments are small and legless. Each pair of legs is slightly longer than the pair preceding them, ensuring that they do not overlap, which reduces the chance that they will collide and trip the animal. The last pair of legs may be as much as twice the length of the first pair. The final segment bears a telson, and includes the openings of the reproductive organs.[2] Centipedes mainly use their antennae to seek out their prey. The digestive tract forms a simple tube, with digestive glands attached to the mouthparts. Like insects, centipedes breathe through a tracheal system, typically with a pair of openings, or spiracles, on each body segment. The spiracles leads to long tracheae and tracheoles that mediate oxygen transport to the organs, except for Scutigeromorpha. In this order the spiracles are unpaired and the trachea short, and oxygen supply is performed exclusively by the respiratory pigment hemocyanin.[5] Some species are able to close their spiracles (occludable spiracles),[6] and a few others in dry environments have evolved a waterproof cuticle.[7] They excrete waste through a single pair of malpighian tubules.[2]