none. During first stages of oogenesis in an ichneumonid wasp Coleocentrotus soldanskii, in each 32 cell cluster, as many as 8 cystocytes enter meiosis. Only one differentiates as an oocyte, the rest are gradually transdetermined to become nurse cells. Significantly, the nurse cells that have passed the first stages of meiosis retain some features characteristic of the oocyte. Namely the nuclei of these cells, as the oocyte nucleus, produce accessory nuclei (AN). Gradual transdetermination of pro-oocytes into nurse cells and the occurrence of ANs in transdetermined cells suggest that a diffusing substance, forming a concentration gradient, is responsible for the determination of the oocyte within the cystocyte groups in hymenopterans.