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the most extensive group of higher insects, including both winged and wingless individuals. In some species, wings develop in the adult stage even though they do not perform the function of flying. A group of Pterygota have wings that are somewhat reduced or absent. Thus, Pterygota includes the bedbug, which is wingless, and the order Hemiptera, which has many species with developed wings. Some species have lost their wings as an adaptation to a specific way of life; however, the structure of their respiratory system, their developmental cycle (fleas), the structure of their mouthparts (bird lice, true lice), and other characters are similar to those of winged insects. Pterygota are marked by a somewhat complex postembryonic development (metamorphosis). They may be divided into two groups—those having incomplete metamorphosis and those having complete metamorphosis.