{Bombyx mori L.)

Embryogenesis in the egg of the silkworm, Bombyx mori, up to 24 h after oviposition was studied, by light microscopy with special reference to nuclear migration and blastoderm formation. In Bombyx eggs blastoderm cells seem to form in a mechanism different from that usually seen in many other insect species; that is, in Bombyx eggs no typical cleavage furrows were seen. Cleavage nuclei which had migrated, accompanied by the associated cytoplasm, to the egg surface pushed up the plasma membrane and protruded beyond the initial level of the periplasm. The periplasm fused with their associated cytoplasm was partitioned among and pulled around the nuclei. Then each nucleus was separated by a laterally-invading limiting membrane from the yolk-granules-occupied region to yield a blastoderm cell