Some Remarks on the Nucleolus Organizer of Drosophila hydei and Rhynchosciara americana (Diptera)

Abstract

The nucleolus forming zones of the polytenic chromosomes of Drosophila hydei and Rhynchosciara americana are studied. It is postulated that the main nucleolus organizer of Drosophila hydei lies in the chromocenter. Those of Rhynchosciara americana are probably located in the four chromosomes, although the main organizer is the centromeric heterochromatin of the X.