Salivary gland development in the blowfly, Calliphora erythrocephala

The salivary gland of adult Calliphora erythrocephala is a tubular structure composed of secretory, reabsorptive, and duct regions. Development of these structures has been followed during the six days of larval and ten days of pupal growth. Two small groups of imaginal cells located at the junction between larval gland and duct give rise to the adult gland. These presumptive adult cells divide during all larval stages and appear to be functional components of the larval gland. Shortly after pupation, the larval gland breaks down and the imaginal cells proliferate rapidly, forming sequentially the duct, reabsorptive and secretory regions. Proliferating regions of the developing gland are frequently encrusted with haemocytes. As it elongates the gland establishes intimate contacts first with the basement membrane of the degenerating larval gland, later with an epithelial layer surrounding the main dorsal tracheal trunks, and then with the gut. Cell division continues until about five days after pupation, bu t the gland is unable to secrete fluid in response to 5-hydroxytryptamine stimulation until two hours after the adult fly emerges. The Golgi complex appears to be involved in forming the highly folded membranes of the canaliculi in the secretory region. Presumptive adult salivary gland cells appear to increase in number logarithmically from the time of hatching of the larva until five days after pupation. This contrasts with the development of classical imaginal discs, in which cell division ceases prior to pupation.