The main structural elements (folds and fields) of folding pattern in beetle hindwings are considered. General trends in their transformation during structural evolution are discussed. The major trend is the complication of the folding system. Its new elements (folds and fields) were formed by stages mainly in centrifugal direction. The origin of field B seems to be the first stage. At the next stage (corresponding to folding types in Archostemata and Adephaga + Myxophaga), field H became fully separate, while field C was not isolated. The final stage was marked by developing the Polyphaga folding type, the characteristic feature of which was the presence of fields C, S, and D. Initially, the D field duplicated the function of the B field, then it fully took it over resulting in the partial or complete reduction of the B field.
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