Abstract
The nuclei of spermatocytes of many (possibly all) species of the genus Drosophila contain peculiar structures which have never been observed in any other stage of the male germ line cells nor in any somatic type of cell. It has been possible to demonstrate that these special structures are, in principle, organized similar to the loops of the so-called lampbrush chromosomes. Thus, the structures are the result of the unfolding of a DNA axis from specific sites (chromomeres) of chromosomes and of the attachment of masses of matrix material, composed of RNA and protein, to this axis. In this way, structures large enough to be visible in the light microscope are formed whose appearance or disappearance are signals for the activation or repression, respectively, of genetic factors (Hess and Meyer, 1963, 1968).
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