Concerning the Origin of the Polytene Chromosomes of Diptera

Abstract

In view of the unprecedented rapidity with which new findings on polytenel chromosomes are being published, it may not be amiss to draw attention to certain aspects which are not very often considered.Polytene chromosomes are known to occur in many larval tissues of Diptera other than those of the salivary gland.They have been recorded in the nuclei of the fat bodies, hypodermis, intestine, absorbing cells of the midgut, muscles, malpighian tubules, tracheal cells and sporadic cells in the brain (Balbiani 1881, Carnoy 1884, Dawydoff 1930, Heitz and Bauer 1933, Geitler 1933a, etc.).2The writer has found that Drosophila larvae, fixed in alcohol, sectioned and stained with Heidenhain's haematoxylin, not only show unmistakable polytene chromosomes in the nuclei of the cells of the salivary glands and malpighian tubules, but frequently carry them also in the fat bodies, gut, hypodermis, some muscle fibers and oenocytes.Indeed, it appears that the large nuclei of those cells fated to histolyze during pupational reorgani- zation all contain polytene chromosomes.3Dawydoff (1930) has indicated