Fine structural features of developing leg discs of the blowfly, Sarcophaga bullata (Parker)

The mesothoracic leg discs of the blowfly, Sarcophaga bullata (Parker) were studied by electron microscopy during the third larval instar. As the peripodial membrane and separation form, the cells of the disc become elongated and perpendicularly oriented toward the separation. The cellular organelles do not undergo significant changes until the late third instar. At this time, there is a significant increase in the amount of granular endoplasmic reticulum and in the number of inclusions, particularly in those cells located more deeply in the disc. Nucleolar enlargement and an increase in the number of mitochondria are also observed at this time. The cells at the border of the disc form a columnar epithelium whose surface develops microvilli‐like projections. These projections. These projections reach their maximum development towards the end of third instar. It is suggested that some of the observed changes may represent a phenotypic expression of secretion of cuticular material.