The early embryonic development of the primitive moth, Neomicropteryx nipponensis lssiki (lepidoptera,...

This paper describes the early embryonic development of Neomicropteryx nipponensis from oviposition to the formation of the inner layer. Newly laid eggs are covered with many hygroscopic, gelatinous masses. The chorion is composed of a porous, spongy exochorion of variable thickness and of a thin endochorion. The eggs have a very thin periplasm and contain large amounts of yolk made of proteid and fatty yolk droplets. The processes of maturation division, fertilization, and cleavage are similar to those commonly found in lepidopteran eggs. The blastoderm of Neomicropteryx is very thin in comparison with that of other lepidopteran eggs. The small circular germ disk is formed on the ventral egg surface. It then invaginates deeply into the yolk to form a sac-shaped germ rudiment. The formation of the germ rudiment and of the embryonic membranes resembles that of swift moths, Endoclita (suborder Monotrysia) and of the caddisfly, Stenopsyche (Trichoptera), but differs from that of ditrysian Lepidoptera. As in other lepidopteran insects, the formation of the inner layer begins after completion of the germ band, which has a bilobed protocephalon and a slender protocorm. Unlike the situation in most lepidopteran eggs, yolk segmentation does not occur in N. nipponensis. During formation of the germ band, hydropyle cells are formed in the dorso-posterior region of the serosa; these are here reported for the first time in the eggs of holometabolan insects.