Fine structure of two types of pleuropodia in Diploptera punctata (Dictyoptera: Blaberidae) with observations on their permeability

Abstract

Fine structural analysis of the 2 types of pleuropodia of embryos of the viviparous cockroach, Diploptera punctata (Eschscholtz) reveals that both organs have vast plasma membrane-mitochondrial complexes, but on opposite surfaces of their cells. The appendage-like pleuropodia on the 1st abdominal segment exhibit mitochondria within microvilli at the outer cell surfaces of the bulb and extension which comprise the bulk of the organ. Lateral surfaces are interdigitated and mitochondria-rich, but the inner surfaces are relatively free of mitochondria and infoldings. The atypical cuticle of the bulb is permeable to several vital dyes but less so than the extension, presumably because of a visibly different cuticle. The second type of pleuropodia, called adenopodia, are of the semi-invaginated type, located on the 9th abdominal segment. These organs have mitochondria within deep infoldings of the inner plasma membrane and along the lateral cell surfaces, but not in the microvilli and infoldings at the outer surfaces. Apical pinocytotic vesicles appear to contribute to the formation of multivesiculate bodies which occur in channels between tightly packed microtubules. It is unlikely that these vesicles mediate the uptake of large molecules from the extra-embryonic fluid because vital dyes do not penetrate the cuticle of the adenopodia. However, silver nitrate reacts strongly at its surface, suggesting the presence of and permeability to chloride. Since the structure of these organs is similar to that of ion and fluid transport tissues, such as malpighian tubules and anal papillae, it is proposed that their function as osmoregulators of embryonic hemolymph and extracellular fluid be investigated.