Spontaneous;egg kidney-or bean-shaped, embryo within it develops only ectodermal organs such as skin, mouth parts, bristles, etc., but no mesodermal ones differentiated, and dies irrespective of its own genotype is ki/ki or ki/+:kic (筑紫腎臓形卵, kidney of Chikushi) and kit(玉沢腎臓形卵, kidney of Tamazawa, induced by low temperature)similar.