Abstract
Naked eggs of the silkworm, Bombyx mori L., which had been stripped of the chorion, were cultured in vitro and inoculated with cytoplasmic-polyhedrosis virus. Embryos grew in these eggs, but the polyhedron formation was observed to occur only in the mid-gut of normally developed embryos which had swallowed down the serosa and reached at the point of stage about to “hatch”. Polyhedron formation could be found neither in the mid-gut primordium nor in malformed mid-guts both of which often came out into the surrounding culture medium as a result of evagination or incomplete dorsal closure of cultured embryos. It seems that per os administration of the virus is, as in larvae, the most effective method for infection of the virus in cultured embryos, and that a certain degree of morphological or physiological differentiation of the mid-gut cells is a necessary factor for the virus infection. Polyhedron fomation was never observed to occur in the eggs which were laid by polyhedron-containing mothers and cultured in vitro without inoculation.
