The comparative submicroscopic morphology of the ring gland of Drosophila melanogaster during the second and third larval instars.

Abstract

A description is given of the ultrastucture of the ring gland of late second and late third instar larvae of Drosophila melanogaster. The organ contains tissues of four types: (1) corpus allatum cells, (2) prothoracic gland cells, (3) corpus cardiacum cells, and (4) tracheal cells. Axons bearing spherical neurosecretory granules pass from the corpus cardiacum to the corpus allatum. Ecdysone and juvenile hormone are thought to be manufactured by smooth surfaced endoplasmic reticulum contained in the prothoracic gland cell and the corpus allatum cell, respectively. The morphology of these cells at the two developmental stages studied suggests that the switch over from larval to pupal development is preceded during the third larval stage by an increasing hormone secretion by the prothoracic gland cells and a decreasing secretion by the cells of the corpus allatum.