The immature instar of an aquatic hemimetabolous insect

Specialized organs, similar to glands, that store their secretory product in a special chamber until stimulated to release it by a signal from the nervous system (or another hormone).

Specialized nerve cells (neurons) that respond to stimulation by producing and secreting specific chemical messengers. Functionally, they serve as a link between the nervous system and the endocrine system.

Dorsal region of a thoracic segment