Junctional structures in the metamorphosing midgut of Aeshna cyanea (Insecta, Odonata).

The metamorphosing midgut of Aeshna cyanea is characterized by the successive development of two tissues: the reticulated tissue and the imaginal epithelium. These tissues supply information concerning contacts between cells diverging in their developmental pathways although arising from the same stem cell population. In addition to small desmosomes, which bind reticulated to imaginal cells, the reticulated cells form invaginations into the apex of imaginal epithelial cells. The projections of the reticulated cells have enlarged tips, and numerous microfilaments run longitudinally along the length of these processes. It is suggested that the anchoring projections of these cells delay the casting off of the reticulated tissue into the lumen, and thus allow the development of the imaginal microvilli. These project into the dilated intercellular space filled with a glycoprotein material that separates imaginal and reticulated cells (Andries, 1972).