Median Neurosecretory Cells and Associated Nerves of the Adult Black Blow Fly, Phormia regina (Diptera: Calliphoridae)

The neuroendocrine system and stomatogastric nervous system of the adult black blow fly, Phormia regina (Meigen), were observed using phase contrast, Nomarski, light, and electron microscopy. No frontal ganglion or ganglionlike structure was found in P. regina . In its place, there is a three-way nerve junction made of two labrofrontal connectives and the recurrent nerve. This junction contains no perikarya; thus, it is nonganglionic. Neurosecretory granules (NSG) are found in some axons of the junction. Two types of neurosecretory cells can be identified in the pars intercerebralis of the brain based on size and electron opacity of their NSG, and their staining reaction with the paraldehyde/fuchsin (PAF) method. Cytoplasm of the A cells contains a large number of NSG of ca. 80-400 nm in diameter and is stained purple with the PAF method. Cytoplasm of B cells contains a smaller amount of NSG of ca. 80-170 nm in diameter and is stained green with the PAF method. Shortly after leaving the brain, the nervi corporis cardiaci (one from each cerebral hemisphere) approach and join with the recurrent nerve to form a larger nerve bundle, the cardiac-recurrent nerve. NSG were found in this larger nerve bundle and in the corpus cardiacum.