Springer Online Journal Archives 1860-2000
Summary The first spermatocyte division has been investigated in Rhabdophaga batatas Walsh and Wachtliella persicariae L. It was shown that the course of this division cannot be described as mitosis, either “unipolar” or “modified bipolar”. Its essential features are: complete absence of pairing and the segregation of the chromosomes into two groups composed of 4 and 30-odd chromosomes. The segregation is accomplished by a peculiar expulsion of the group of 4 chromosomes from the main nucleus followed by an unequal cytokinesis. The spindle is absent and the nuclear membrane remains present during the entire course of the division. The second spermatocyte division occurs only in the smaller cell, which contains 4 chromosomes and bears all features of normal mitosis. For the description of the course of the first spermatocyte division and chromosome distribution, which occurs in this division, the terms “segregating division” and “monocentric configuration” were proposed. The available descriptions of the first spermatocyte division in other species of Cecidomyiidae have been analyzed. The pattern of this division in all so far investigated cecidomyiid species is very uniform and the terms “unipolar” or “modified bipolar” mitoses are here also inadequate. The cases were discussed in which the peculiar chromosome arrangements arise merely as a result of positive or negative interrelations between the centriole and the chromosome parts. With this as background, the monocentric configurations in Cecidomyiidae were explained in terms of an attraction between the centriole and centromeres, operating in one group, and a repulsion between the centriole and the chromosome ends acting in the second. The other so-called unipolar mitoses have been analyzed. It was shown that under this term at least three intrinsically different configurations have been described. For the cases of Sciara, Micromalthus debilis and Cecidomyiidae, the common denominator can be found: the chromosome movements in Sciara and M. debilis can also be explained as set forth above for Cecidomyiidae, i.e. in terms of two kinds of forces operating between the centriole and the chromosomes. The several spindle fibers present in Sciara and Micromalthus do not seem to be crucial for the chromosome movements.
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