Abstract
1) The first meiotic divisions from prophase to metaphase in various species of orthopteran spermatocytes were studied by means of phase-contrast cinematography using an oil immersion lens.
2) The development of the chromosomal spindle fibers revealed by the observation on the first spermatocytes of Gastrimargus transversus as well as Patanga japonica is as follows. At the late diakinesis of these cells, near the nuclear membrane, two centrioles become visible from which both the astral rays and the presumptive chromosomal spindle fibrils radiate. The latter fibrils, not different in structure from the astral rays and radiating only towards the nucleus, are brought into contact with the nuclear membrane. The disappearance of the membrane initiates at the portions with which these fibrils are in contact. The fibrils grow into the nucleus through thus disrupted portions of the nuclear membrane and become attached to the kinetochores of the chromosomes. And it could be observed that each of the chromosomal spindle fibers was composed of a number of fibrils which were formed in above-mentioned way between the centers and the kinetochores.
3) The movement of the chromosomes towards the nuclear periphery which takes place shortly before the disappearance of the nuclear membrane and the ensuing movement towards the developing spindle were found in the first meiotic division of all the orthopteran spermatocytes studied. And the movement towards the developing spindle cannot be explained by the pushing action of the spindle fibers alone which grows from the poles to the equator in the same period, besides, other factor or factors may be concerned as well.
4) Some of the kinetochores of univalent and paired chromosomes can change their orientation from one pole to the other before their co-orientation (re-orientation). In addition, even if the co-orientation of a bivalent is completely interrupted in prometaphase, the bivalent can enter a second coorientation (re-coorientation). In the process of this second co-orientation, the chromosomal fibers which have been dissoluted to some extent might be reversibly reconstructed between the poles and the kinetochores of the bivalent.
