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Quarterly Journal of Microscopical Science, Vol s3-93, 475-486, Copyright © 1952 by Company of Biologists

Enucleation of Sea-Urchin Blastomeres with or without Removal of Asters

I. JOAN LORCH 1

1 Department of Zoology, King's College, London, W.C. 2

The following experiments were carried out on one blastomere at the two-cell stage of the sea-urchin egg:

1. Removal of the nucleus.

2. Removal of the nucleus and surrounding cytoplasm (centrosphere).

3. Attempted removal of the centrosphere only.

In cells from which the nucleus had been removed the asters multiplied for up to 7 hours and then disappeared. During the period of aster multiplication, cleavage furrows often appeared between the asters but did not succeed in dividing the cell. After about 8 hours, cleavage into a large number of spheroidal cells occurred. When the nucleus and centrosphere were removed no asters were formed and no cleavage furrows were observed until after about 8 hours, when division into a large number of spheroidal cells occurred.

When attempts were made to remove the centrosphere, leaving the nucleus intact, asters were always eventually re-formed Before the re-formation of asters neither the nucleus nor the cytoplasm divided although dissolution of the nuclear membrane, followed by its reappearance, occurred. After re-formation of the asters cleavage appeared to be normal.






© The Company of Biologists Ltd 1952