Hemipteran insects have highly specialized mouthparts for extracting liquid food from plant or animal tissues; these consist of two pairs of stylets (mandibular and maxillary) enclosing two canals (alimentary and salivary). The stylets are sheathed inside a fleshy proboscis (a labial rostrum) which is directed posteriorly at rest; palps and cerci are absent. The wings develop externally (exopterygote development). The forewing may be thickened in its basal half to form a hemelytra (a feature of Suborder Heteroptera); wing reduction or absence is common. The immature stages usually resemble small adults (hemimetabolous development).