A Coat of Repeating Subunits on the Cytoplasmic Surface of the Plasma Membrane in the Rectal Papillae of the Blowfly, Calliphora Erythrocephala (meig.), Studied in Situ by Electron Microscopy

Structures associated with the rectum of insects, e.g., rectal papillae, rectal glands, rectal pads, are believed to be concerned with an active uptake of water and ions from rectal contents (1-7). In the blowfly, rectal papillae are 4 hollow cones with their tips projecting into the rectal wall and their bases facing the haemolymph. The wall of each cone is formed by a single layer of columnar epithelium, but the concavity is filled with tracheae and connective tissue cells containing many nerve endings (8, 9). Our studies have revealed that, in essence, the epithelial cells have the same organization that Copeland (10) described in the sodium-transporting anal papillae of a mosquito larva. However, the structures he designated as "mitochondrial pumps" are far more numerous and complex in this material and are associated with the lateral plasma membrane of the cells (11, 12). The apical surface (facing the lumen) of the papillae is lined by a cuticular intima, and the underlying plasma membrane of the epithelial cells is highly infolded to form "leaflets" (11). In all our electron micrographs, the cytoplasmic surface of this apical plasma mere-