part of continuous with develops from prothoracic gland FBbt:00001724 fly_anatomy.ontology PTG Component of the larval ring gland that is continuous with the corpus cardiacum at its ventroposterior end, encircles the aorta, and surrounds the medially-located corpus allatum at its dorsoanterior end (Dai and Gilbert, 1991; de Velasco et al., 2004; Nassel and Zandawala, 2020). It is composed of very few cells in the late embryo, but these increase in size and number during larval development (de Velasco et al., 2004). It produces ecdysone and is most active in the early wandering third instar (Dai and Gilbert, 1991; Nassel and Zandawala, 2020). During pupal development, its cells separate, shrink and degenerate and none are found attached to the adult corpus allatum or corpus cardiacum after eclosion (Dai and Gilbert, 1991). thoracic gland embryonic/larval corpus allatum embryonic/larval corpus cardiacum prothoracic gland primordium neurohemal organ dorsal ectoderm derivative larval ring gland