Effect of Colchicine and cytochalasin B on ooplasmic segregation of ascidian eggs.

Ooplasmic segregation inPhallusia mammillata was completed 3 to 5 min after fertilization. Colchicine, which completely stopped nuclear divisions, did not inhibit segregation. Cytochalasin B, which prevented cleavage at a low concentration (0.2 μg/ml) inhibited segregation only at a concentration at least five times higher. The action of these drugs leads to the conclusion that ooplasmic segregation does not depend on an assembly of microtubules or on microfilaments which are involved in cell division.