The stomatogastric nervous system and the ring gland consist of several small clusters of neuroendocrine elements situated posterior to and between the two cerebral hemispheres, in association with the pharynx, oesophagus and proventriculus, dorsal pouch and aorta. Due to the small size of the various ganglia of the stomatogastric nervous system, their identification in the Drosophila embryo is difficult. However, the available markers have allowed identification of homologs to the ganglia found in other, larger insects (Fig. 10.1). The ring gland comprises the corpora cardiaca, the thoracic glands and the corpus allatum. The following description is largely based on Hartenstein et al. (1994a), Gonzalez-Gaitan et al. (1994) and Gonzalez-Gaitan and Jackle (1995).