Abstract
Four interpretations of salivary gland chromosome structure have been proposed which are based on the assumption of microscopically visible chromonemata here. Two have been abandoned (that of Alverdes and that of Koltzoff and of Bridges). The remaining 2 (that of Bauer and that of Painter and Griffen) are mutually exclusive. Evidence indicates that neither of these is correct. Although chromonemata may readily be seen under the microscope in many "ordinary" mitotic chromosomes, such chromonemata should be of sub-microscopic thickness if extended to the length of salivary gland chromosomes. Likewise, there should be a thousand or more present. Numerous lines of evidence are reviewed in support of the view that the pattern in these chromosomes is not made up of visible chromonemata, but reflects the type of structure postulated by Metz and Lawrence. The latter view also serves to explain the widely different interpretations given by the other authors.

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