In Drosophila hydei, the so-called lymph gland is shown to be the exclusive source of oenocytoid cells (= lamellocytes). Inasmuch as in Insect hematology these cells are considered to be true elements of the circulating hemolymph, the gland is thus a hemopoïetic organ. Oenocytoid hemocytes appear for the first time in third-instar larvae at the age of 150 h. They increase in numbers toward the end of the larval period, but the bulk of the cells is discharged during metamorphosis whereby the organ disappears. The lymph gland appears to be essentially a pupal organ. The fonction of oenocytoid hemocytes and thus of the organ remains to be elucidated.