Accessory nuclei were observed in early meiotic prophase (leptotene) in female Ascaris suum but such structures were absent in meiosis in males. Accessory nuclei also were observed during the prediminution embryonic divisions. All embryos did not have accessory nuclei, thus, those embryos with these structures may be female since the accessory nuclei are maternal-limited. Accessory nuclei were not observed after the fourth embryonic division, at which stage the process of chromatin diminution begins. The eliminated chromatin may be composed in part of DNA from accessory nuclei.