THE ABSENCE OF CHIASMA TERMINALIZATION AND INVERTED MEIOSIS IN MALES AND FEMALES OF MYRMUS-MIRIFORMIS FN (CORIZIDAE, HETEROPTERA)

Terminalization of chiasmata and orientation of bivalents were analyse d in males and females of Myrmus miriformis Fn. (Corizidae, Heteropter a). In spermatogenesis, the frequencies of the largest autosome bivale nt with medial, subterminal and terminal chiasmata were compared at di plotene, early and late diakinesis and metaphase I. The bivalent displ ayed a single subterminal or medial chiasma in nearly 90 per cent of c ells at diplotene. The frequency of such bivalents was still over 80 p er cent at metaphase I, indicating the absence of complete chiasma ter minalization. It is possible that chiasmata do not terminalize at all. In oogenesis, all bivalents at metaphase I displayed subterminal or m edial chiasmata, indicating that terminalization is also absent in fem ales. In both males and females all bivalents co-orientated at metapha se I, the telomeres of homologous chromosomes being orientated towards opposite spindle poles. Hence, they underwent prereduction in meiosis ; no evidence for an inverted meiosis could be found.