Unique chorion structure of the mottled gray (mgr) egg, an egg-character mutation of Bombyx mori (Lepidoptera : Bombycidae)

The surface and internal chorion structures of the mottled gray egg (mgr) o f Bombyx mori, a mutation which exhibits patched areas of gray or opaque re gions, were observed in comparison with normal eggs using a scanning electr on microscope. No peculiarity was exhibited in the mutant with respect to w hole egg size, surface structures at the micropyle region and basic pattern s as well as the average area of the network imprints (polygons) on the lat eral flat region. When cross-sections of the chorions were observed, the mi ddle layer of the mgr chorion corresponding to the gray areas was found to be deformed without a lamellar structure. Thus it can be concluded that the mgr alleles take part in the formation of the middle layer architecture du ring choriogenesis.