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two successive indirect divisions of developing sex cells in animals and plants that reproduce sexually. As a result of maturation division, the number of chromosomes (characteristic of somatic cells) is reduced to one half the original number in the nuclei of sex cells. Maturation division in male sex cells precedes the formation of mature spermatozoa. In female sex cells it halts at different stages, depending on the type of organism, and is usually completed in the fertilization period after the egg has been activated.