Main structural elements (folds and fields) of the folding pattern in beetle hind wings are considered, and general trends in their evolutionary transformations are discussed. The major trend consists in increasing the complexity 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 the folding types found in Archostemata and Adephaga + Myxophaga), field Hbecame fully separate, while field C was not isolated yet. The final stage was marked by the development of the Polyphaga folding type, whose characteristic feature was the presence of fields C, S, and D. Initially, field D duplicated the function of field B and later took it over, which resulted in partial or complete reduction of the latter.
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