Cellularization During Embryogenesis in <I>Thermobia domestica</I> (Zygentoma: Lepismatidae)

Abstract

During the first day of embryogenesis in firebrat, Thermobia domestica (Packard) (Zygentoma: Lepismatidae), energids (nuclei surrounded by a thin layer of nonmembraned cytoplasm) migrate toward the periplasm. Some of them are dispersed in the periplasm, whereas others remain inside the yolk. As the first syncytial blastoderm is formed, the oolemma invaginates deeply into the yolk forming numerous folds. These folds surround the energids that are settled in the periplasm. The cellular blastoderm, formed at the end of cleavage, remains thin. These cellularization events are described at the ultrastructural level. Our previous studies dealt with midgut epithelium formation. Our current results indicate that the same mechanism of cellularization occurs in both processes in this primitive wingless insect. The similarities between the mode of cellularization of the blastoderm and the midgut epithelium are discussed.