Degree Name

Master of Science (MS)

Semester of Degree Completion

1978

Thesis Director

William S. James

Abstract

Lehman's polychrome stain was used to follow the fate of germinal plasm in early development of Bombina orientalis embryos. Islets of germinal plasm approximately 6 um in diameter were observed in the vegetal pole region of the 2-cell embryo. By the 4-cell stage, some of these islets had coalesced to form larger ones so that two size classes of islets were present (approximately 7.5 and 19.5 um in diameter).

As cleavage continued to the 16-cell stage, the islets were moved further up the cleavage furrow and were always observed to remain in close association with the cleavage membrane. The islets at this time had reached a diameter of approximately 32 um. In the 32-cell embryo, the cells that contained germinal plasm and that were also adjacent to the developing blastocoel, exhibited a protuberance of cytoplasm consisting of pigment, yolk and germinal plasm.

At the mid-to late blastula stage, the germinal plasm was contained in a few cells located in the lower one-third of the embryo. The peripheral position of the germinal plasm was maintained in these cells. During early gastulation, the germinal plasm began to migrate from its peripheral location to a juxtanuclear position.

Examination of neurula and early tail bud stages did not reveal any cells containing germinal plasm. The implication was that the germinal plasm may have been utilized previously to these stages. At the time of opercular closure (which is an equivalent stage to Shumway stage 25), there were approximately 61 primordial germ cells in the dorsal mesentery and genital ridges.

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