Abstract
In the primary spermatocytes of Lasiopogon (species not yet determined) the earliest growth stages resemble those in other asilids (e.g., Asilus sericeus); 1 but before growth has progressed very far, the nucleus, which previously has been approximately spherical, becomes irregularly invaginated and evaginated. The nuclear membrane appears to push in around the chromosome threads and the latter to push out into the cytoplasm; so that soon each thread (bivalent) lies in a lobe or pocket, isolated to a great extent from the others. The nucleus becomes converted almost entirely into lobes, which follow the contour of the chromosomes and ramify in various directions through the cytoplasm. There is no uniform configuration; the chromosome threads are long and slender, and often follow a tortuous path, apparently at random save for a slight polarization toward the nucleolus.
As growth progresses the chromosome threads condense and shorten, and coincidently the lobes become less ramifying. This process continues up to the metaphase of the first division, when the chromosomes are fully condensed. The nuclear outline is still persistent at this time and still exhibits an irregular contour, conforming to that of the five bivalent chromosomes.
Aside from the unusual nature of these processes, which, so far as we know, have not hitherto been found in maturation stages, two features appear to be of interest. First is the fact that as the nuclear membrane (or the cytoplasm) pushes in around the chromatin threads, it comes close to, but not in contact with, the threads. This is easily seen, for the nucleoplasm is transparent and the cytoplasm is dark, leaving the boundary, or nuclear membrane, clear cut in outline. If the lobe is cylindrical, as is frequently the case, the chromatin thread extends uniformly through the center (or near the center), like a slender core.
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