Abstract
The morphological and biological nature of the supravitally recognizable metachromatic granules in living and fixed sea urchin egg following fertilization and during cleavage were investigated by means of light (supravital staining and semi-thin section) and electron microscopy.
Within the egg plasm of living unfertilized eggs one can perceive a small number of metachromatic granules stainable with toluidine blue O which appeared diffusely among yolk granules. But during the segmentation stage they appeared principally within the astral region and increased in number similar to the “β-granules” of PASTEELS as well as the “aster-associated particles” of REBHUN.
In the semi-thin sections (fixed with OsO4, embedded in epoxy resin, 0.5-1.0μ in thickness, stained with toluidine blue O), there could also be recognized abundant metachromatic granules within the astral region. The granules seemed to be identified with the metachromatic granules in the living egg.
Furthermore, as revealed with the electron microscopy, two types of granules which were identified with the metachromatic granules were recognized. It has been suggested, thereafter, that these granules might be derived from certain yolk granules following structural and chemical changes contrary to the concept of REBHUN. Moreover, it should be emphasized that the biological role of the granules may be intimately related to an energy producing mechanism for the progress of egg segmentation and cell differentiation.
