An electron microscopic investigation of the Malpighian tubules of a leaf hopper, Macrosteles fascifrons, shows that these organs comprise three quite distinct cell types, and the structure of these and of the mid- and hindgut epithelial cells is described. In particular, a comparison is made between the organization of the basal and apical surfaces of cells in the Malpighian tubule and in the vertebrate kidney, and it is suggested that similarities between these excretory epithelia reflect functional parallels between them. While the midgut and one region of the Malpighian tubule bear a typical microvillar brush border, elsewhere in the tubule and in the hindgut the apical surface bears cytoplasmic leaflets or lamellae. The sole solid excretory material of these insects consists of the brochosomes, secreted by cells of one region of the Malpighian tubule. The structure, geometry, and development of these unusual bodies, apparently formed within specialized Golgi regions, has been investigated, and histochemical tests indicate that they contain lipid and protein components.

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