THE EARLY EMBRYONIC-DEVELOPMENT OF THE MNESARCHAEID MOTH, MNESARCHAEA-FUSILELLA WALKER (LEPIDOPTERA, MNESARCHAEIDAE), AND ITS PHYLOGENETIC SIGNIFICANCE

Formative processes of the blastoderm, germ disk, germ rudiment and em bryonic membranes in the mnesarchaeid moth, Mnesarchaea fusilella, are described, and their phylogenetic significance is discussed. The egg is ovoid, about 0.32 mm by 0.48 mm in size. Below the thin chorion lie s a very thick vitelline membrane. In the newly laid eggs, this membra ne is colourless, but it becomes blackly pigmented about 30 hours afte r oviposition. Soon after the completion of the blastoderm, the germ d isk or embryonic area forms in the posteroventral region of the egg. I t then invaginates into the yolk, and becomes a sac-shaped germ rudime nt. After closure of its opening, the germ rudiment separates from the rudimentary serosal or extra-embryonic area Its inner region later de velops into the embryo, and its outer one into the amnion. The serosa is thick and each of its cells has two nuclei. The formative process o f the germ rudiment and embryonic membranes in M. fusilella is primiti ve and very similar to that of the hepialid moths, Endoclita excrescen s and E. sinensis. From the embryological standpoint, Mnesarchaea clea rly belong to the Exoporia because of the following two synapomorphic characters: (1) formation of the thick, blackly pigmented vitelline me mbrane: and (2) presence of thick, bi-nucleated serosal cells.