Fig. 35. Oogenesis of a Nematode Worm (Ancyracanthus). A, egg mother cell containing 12 chromosomes before their union into pairs; B, early stage of first maturation division; all the chromosomes have united into 6 pairs, each of which has split in two so that the pairs are really four-parted (tetrads); C, the six tetrads in the first maturation division; D, egg containing 6 chromosomes, after both first and second maturation divisions; the eliminated chromosomes are shown as the polar bodies at the margin of the egg; E and F, eggs after fertilization; the egg nucleus is above and contains 6 chromosomes, the sperm nucleus below and contains 5 chromosomes in one case and 6 in the other; the former becomes a male with 11 chromosomes, the latter a female with 12 chromosomes.