Studies on the yolk granules of the silkworm,Bombyx mori L.: The morphology of diapause and non-diapause eggs during early developmental stages

Summary The morphological features during development of diapause and non-diapause eggs of the silkworm,Bombyx mori, were investigated by means of light and electron microscopy, with special reference to eggs up to 24 h after oviposition.The blastoderm and yolk cells began to be formed about 6 and 24 h after oviposition, respectively, in both the diapause and non-diapause eggs, indicating that the diapause and non-diapause eggs develop at similar rates at least until 24 h after oviposition.Specific changes in the distribution of yolk granules were observed during early development of the diapause egg. Its yolk granules gradually aggregated into clusters from the periphery toward the inside of the egg during the period of blastoderm formation. Aggregation of yolk granules was most noticeable about 12 h after oviposition and then they dispersed again before yolk cell formation. On the other hand, yolk granules of the non-diapause eggs remained dispersed during development.