Fig. 2. Malpighian tubules of the yellow fever mosquito Aedes aegypti. The tubule presents two types of cells, principal cells and stellate cells, in a ratio of 5:1. (A) Principal cells are characterized by large intracellular concretions (spherites) of organo-metallo complexes of Ca²⁺, Mg²⁺ and K⁺ and by long slender microvilli containing mitochondria. (B) Stellate cell bracketed by principal cells. Stellate cells do not contain intracellular concretions and their brush borders are short and devoid of mitochondria. The basolateral membrane facing the hemolymph shows extensive infoldings. Septate junctions define the lateral border with principal cells.