POLARIZATION, KINETOCHORE MOVEMENTS, AND BIVALENT STRUCTURE IN THE MEIOSIS OF MALE MANTIDS

¹ Department of Zoology, Columbia University

1. Bouquet formation. An analysis of the second polarization or bouquet stage in the meiotic prophase of the males of several species of mantids shows bouquet formation to be a special process, basically distinct from the relic or Rabl orientation, and involving special activities of chromosome ends, division centers, and nuclear membrane.

2. Kinetochore movements. (a) The initial separation or "repulsion" of the homologous kinetochores in the meiotic bivalent is shown in several species to be independent of division centers and spindle and appears to be autonomous to the kinetochores. (b) The pre-metaphase poleward movement of kinetochores and consequent stretching of the meiotic chromosomes are in part due to the elongation of the spindle, and in part to another factor or factors which may include kinetochore repulsion, kinetochore-center attraction, and a special activity of the half spindle components. (c) Resumption of coiling after the pre-metaphase stretch results in the re-approach of the homologous kinetochores and their movement away from the poles. (d) Movement of chromosomes to the equator regularly overlaps the movement (c) above, and may overlap (b), thus excluding any hypothesis of metaphase plate formation in which the chromosomes are regarded as passive.

3. Chiasmata and bivalent structure. Three separable factors in the late meiotic association of homologous chromosomes can be distinguished: (a) lateral attraction, which is independent of chiasmata and is variously localized in different bivalents; (b) terminal attraction which operates in some bivalents quite independently of chiasmata, and in others follows chiasma terminalization; and (c) the action of chiasmata. Absent in late prophase and metaphase in certain bivalents, the presence of chiasmata is inferred in others from the frequency of open cross configurations. These three factors may act more or less separately, and in various combinations, even in closely allied species, and in different bivalents of a single species.

4. Males of Stagmomantis carolina from Virginia and from Barro Colorado Island, C. Z., identical taxonomically and in chromosome complement, differ in the time of spindle formation relative to the stage of bivalent development in the meiotic prophase.