The appearance of a type of cortical vesicles subsequent to fertilization of the sea urchin egg, their character and possible function.

Three different types of vesicles present before fertilization in the sea urchin egg were examined. The "a-type" corresponds to rough endoplasmic vesicles; the vesicles of "b-type" are rather smooth but may have vestigial granules within their membranes; the "c-type" belongs to the multivesicular bodies. Upon fertilization, vesicles appear in the outer cortical zone (vesicles of "d-type"). The majority of them arises by budding from the vesicles ofb-type. The budding occurs mainly at the basis of or within ridges of the cell surface; they may also be present in broader microvilli. The distance between the ridges was varied by early transfer of the eggs to calcium-free sea water. An inducing effect of the ridges on location of theb-vesicles and on the formation ofd-vesicles by budding could thus be demonstrated.Thed-vesicles appearing upon fertilization resemble in size and structure Golgi vesicles formed by budding from Golgi bodies present in the interior cortex or below it. Also theb-vesicles have their counterpart in the Golgi bodies. Theb andd-vesicles are therefore regarded as a Golgi system in which theb-vesicles represent dispersed Golgi bodies and thed- vesicles Golgi vesicles. Thed-vesicles may be designated as cortical Golgi vesicles, (c.G.v.).In thec-vesicles i.e. the multivesicular bodies (m.v.b.), a nucleid was observed which may be subdivided. A compartmentation of m.v.b. was observed which may lead to a detachment of vesicles of about the same size as thed-vesicles (c.G.v.) but probably of a different character.The differentiation of the fertilization membrane of the sea urchin egg occurs in two stages: the assembly and the solidification stage. The tentative conclusion is drawn that a secretion from the c.G.v. functions as an agent in the solidification process. The c.G.v. may also act upon the hyaline layer, both in its early formation and its maintenance during the course of embryonic development.