The changes which most likely occurred in the egg to cause accidental and obligatory parthenogenesis have been discussed. As regards obligatory parthenogenesis, in the case of restoration of diploidy by alteration of meiosis (that the Author calls intrameiotic regulation), it has been assumed that the stages of meiosis following the sperm entry into sexual eggs could have been more easily modified than those preceding it. Finally it has been pointed out that in heterogonic species the preservation of somatic chromosome number by endomeiotic and ameiotic regulation should be due to the influence of internal female conditions but not to mutations affecting meiosis.
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Con il contributo del Ministero per i Beni e le Attività Culturali