抄録
1) The reduction division is an extreme modification of the normal mitosis, in which the chromosome division is suspended. The cases of the free nuclear division, the endomitosis and the salivary chromosome formation are regarded as other modifications in smaller degrees linking, in some loose sense, both extreme cases, the mitosis and the reduction division, in the order named.
2) In the reduction division, the regular polar chromosome, separation takes place by replacing the chromosome doubling-bydivision with that by pairing. If the chromosomes paired are sisters, the result is the somatic reduction, and if they are homologues, it is the meiotic reduction.
3) Morphologically, the meiosis is a mitosis in the prophase of which the meiotic reduction division takes place, and therefore, the first meiotic prophase is a double prophase, and the whole cycle of the meiosis is the cycle of a double mitosis in the sense that the reduction division is a modified mitosis.
4) In meiosis, physiological conditions should differ from those in the normal mitosis. These conditions may cause the chromosome pairing which gives rise to the double prophase or the prolongation of prophase that may upset the time relationship between the chro-mosome development and the spindle formation, thus resulting in the disjunction of the paired chromosomes instead of the separation of the divided chromosomes and in the occurrence of an extra polar chromosome separation which separates the latter to complete the division. The cycle of the double mitosis is thus completed, and further mitoses need not follow necessarily.
5) The theories of meiosis are reviewed and an alternative or a modification is suggested based on DARLINGTON'S principle of attraction between single chromosomes and repulsion between pairs of pairs, modifying it by adopting instead of the actual singleness an apparent singleness resulting from the lateral union of the chromatids as a response to the physiological condition in the early prophase of meiosis. The drawn out state of the leptotene or pairing threads is also considered to be responsible for the completion of pairing.
