Chromosomal structure in primary spermatocytes of the locust
During the early to middle diplotene stages of meiotic prophase, the chromosomes in locust spermatocytes contain a pair of dense fibrils, each about 250 Å thick, running parallel to the long axis of the chromosome. These fibrils usually appear to run parallel to each other, 700 Å apart (centre to centre); they have occasionally been observed twisted around each other in a very loose spiral. In some preparations there appears to be a third fibril running midway between the two fibrils just described above; this central fibril is thinner (about 100 Å thick), and less well-defined than the outer pair. All these fibrils, considered together, form only a small part (of the order of 0.5 per cent by volume) of the chromosomal substance.