In these embryos, the lone individual duct is almost always malformed. The individual duct precursors, instead of invaginating, remain in a group and move anteriorly as head involution occurs. In these mutant embryos, the anterior end of the salivary glands is sealed so that the gland resembles a closed sac with no connection to the mouth. There are no other visible defects in the salivary glands. Even when no individual ducts form in eyg -mutant embryos, the common duct can still form, although it does not connect to anything at its posterior end.
Additional tests show that the presumptive individual duct cells become converted to common duct.
In summary, in eyg -mutant embryos, the duct primordia fail to converge and extend across the midline resulting in the absence of individual ducts. The precursors of many adult Drosophila tissues are set aside during embryonic development. These cells multiply during larval development and do not differentiate until metamorphosis. For salivary glands, the adult precursor is a ring of cells at the junction of the salivary gland and the individual duct. During larval growth, the imaginal ring cells remain diploid while both the salivary gland and duct cells become highly polyploid.