Hybridization tests have shown that four Australian morphospecies of the subgenus Pholadoris, genus Drosophila (D. novopaca Mather, D. cancellata Mather, D. lativittata Mall., and D. enigma Mall.), are biospecies, but that the following combinations yield adult offspring: D. novopaca X D. lativittata both ways, D. novopaca X D. cancellata both ways, B D. novopaca X @ D. enigma, and B D. cancellatu X @ D. lativittata, and that "gene exchange" is possible between D. cancellata and D. novopaca under laboratory conditions. Sexual isolation, hybrid inviability, and hybrid sterility all play a part in keeping the species distinct from one another. The results of the hybridization tests support the hypothesis that the species should be placed in one species group (coracina) as was previously done on morphological criteria. Of the three main morphological characters used for separating these species, viz. thoracic, abdominal, and wing markings, those of D. novopaca are dominant to those of D. cancellata. These character differences between at least D. novopaca and D. cancellata seem to be controlled by one sex-linked gene.