Fine Structure and Differentiation of the Midgut Epithelium of Allacma fusca (Insecta: Collembola: Symphypleona)

T he midgut ep i the l ium of insects is responsible for enzyme production, digestion, secretion, and in insects devoid of Malpighian tubules, excret ion (Pac l t 1956, Anderson and Harvey 1966, Humbert 1979, Chapman 1998). These functions are possibly due to the characteristic ultrastructure of epithelial cells which form the midgut epithelium. In the majority of insects, their cytoplasm has distinct regionalization in organelle arrangements, and as a consequence, basal, perinuclear, and apical regions appear (Klag et al. 2002, Rost 2006a b, Rost-Roszkowska et al. 2007a). The midgut epithelium is formed during embryogenesis or less commonly, during larval stages (Dallai 1966, Krzysztofowicz et al. 1973, Rost et al. 2005, Rost-Roszkowska et al. 2007a b). In the middle of larval development, together with the growth of insect bodies, the midgut epithelium is formed by an increasing number of cells.