The structure and salivary function of the labial gland in adult Manduca sexta

The labial gland of the adult sphingid moth, Manduca sexta, consists of five distinct regions, each composed of a single cell type. The morphology of the cells and preliminary physiological evidence indicate that the regions function sequentially in the production of protein (invertase), fluid secretion, conduction of the resulting mixture, salt reabsorption, and storage or release of the final saliva. The morphological adaptations of the cells to their respective functions are discussed.