Fig. 5a-c: B-chromosomes in Phaulacridium marginale. (All photographs are of acetic-orcein preparations, x 1000.) (a.) Pachytene: The B-chromosome can be seen to consist of a large block of heterochromatin, a section of euchromatin, and a small, terminal heterochromatic segment. (Heterochromatin is indicated by h, and the euchromatin by e.) (b.) Diplotene: Although contraction of the bivalents has occurred, the three elements of the B-chromosome are still obvious (arrow). (c.) Metaphase I: The cell has two B-chromosomes which are segregating to the same pole.