Ultrastructure of the Secretory Inclusions of the Salivary Gland Cell in Drosophila

The salivary gland cells of dipteran larvae, particularly the various species of Drosophila, have been of unusual interest to studies in genetics as well as investigations in cell differentiation. The giant polytene chromosomes in the nuclei of these cells have favored extensive cytogenetic analyses, and more recently the phenomenon of regional puffing of the salivary gland chromosomes has been equated to visualization of gene activity (1). The specific cytoplasmic phenotype of these cells in fly larvae may be described in terms of mucoprotein inclusions which are continuously elaborated and accumulate during the period of larval development. One of the known functions of the salivary glands of these larvae is the formation of a muco-protein which at a specific stage of development is discharged into the lumen of the gland. At the time of puparium formation this mucoprotein is expectorated and serves as a glue (2) for adhesion of the puparium to its substratum. A preliminary