An electron microscopic study of the neurosecretory pars intercerebralis--corpus cardiacum system in larvae of the dragonfly, Aeschna cyanae (Müller) (Odonata: Aeschnidae).

The ultrastructural morphology of the medial neurosecretory cells of the pars intercerebralis region of the brain and that of the corpus cardiacum (C) has been described. The medial neurosecretory cells (MNC) are classified as four distinct cell-types--MNC1, MNC2, MNC3 and MNC4 containing the neurosecretory granules (NSG) about 1900 A, 2100 A, 1600 A and 1750 A in diameter, respectively. The varying amounts of NSG have been seen in the axonal tracts, nervi corporis cardiaci and axon terminals in the CC and aortic wall. Two types of intrinsic neurosecretory cells (INC) can be distinguished in the corpus cardiacum--INC1 and INC2 containing the electron dense granules of 3000 A and 2000 A in diameter, respectively. The subcellular mechanisms associated with synthesis and release of the neurosecretory material are discussed.