Morphological Analysis of Eggshell in the Shirotae-ran Mutant, vit, Bombyx mori

The morphology of the eggshell (chorion) of the shirotae-ran mutant, vit (wherein the yolky substances are poor), of Bombyx mori was observed by scanning electron microscopy and differential interference contrast microscopy. The egg size was slightly smaller in the mutant than in the normal. The surface structures of the micropyle in the anterior pole region and the basic patterns of the network structures (polygons) imprinted on the lateral flat surfaces as well as the mode of distribution of the small knobs in the posterior, ventral and dorsal regions exhibited no peculiarity in the mutant. The polygons were significantly smaller in size in the mutant than in the normal. However, the number of polygons per whole lateral side did not differ between the mutant and the normal. The cross section of the mutant chorion was as usual in terms of layer structure and thickness. These findings imply that the choriogenesis occurs ordinarily in the vit mutant.