THE ULTRASTRUCTURE OF THE PROTHORACIC GLAND CORPUS ALLATUM CORPUS CARDIACUM RING COMPLEX OF THE AUSTRALIAN SHEEP BLOWFLY LARVA LUCILIA-CUPRINA (WIED) (INSECTA, DIPTERA)

The ultrastructure of the constituent endocrine glands within the ring complex of Lucilia cuprina larvae has not been previously described. This study investigated the ring complex of mid-third instar larvae. T hree distinct endocrine cell types were identified: (1) prothoracic gl and (PTG) cells which constituted the major cell type; (2) corpus alla tum (CA) cells, localized in the anterior central region, and (3) corp us cardiacum (CC) cells, located posteriorly, ventral to the aorta. PT G cells were identifiable by their large ovoid nuclei (9-14 mum dia, l ength 12-18 mum) and numerous cytoplasmic lipid vacuoles. The plasma m embrane of peripheral PTG cells were invaginated to form intercellular channels. The CA cells are characterized by ovoid nuclei (6-7.5 mum d ia, 6.5-9 mum length) and electron dense staining cytoplasm. Compared to PTG cells the CA cells had smaller nuclei and lower nucleus:cytopla sm cell ratio. Extensive networks of highly irregular, electron-lucent intracellular spaces, dispersed throughout the cytoplasm were also ch aracteristic of CA cells at this developmental stage. These spaces oft en contained membrane bound lipid vacuoles occurring singly or as aggr egates. The CC contained both intrinsic and extrinsic neural component s. The intrinsic cells were characterized by circular nuclei (6.5-8.5 mum dia), prominent nucleolus and numerous cytoplasmic electron-dense neurosecretory granules (100-240 nm dia). The extrinsic axons and term inals within the CC contained electron-dense neurosecretory granules ( 80-150 nm), neurotubules and mitochondria.