. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 122 V. C. ABRAHAM ET AL. Figure 8. Formation of second polar body and pronuclear migration. Untreated eggs (A-C) and eggs treated with 100 colchicine (D-E) were fixed at tn = , subsequently stained with Hoechst 33258, and viewed with either phase contrast (A. D) or epifluorescence (B, C, E) optics. The second polar body (arrowhead) could be seen near the animal pole in both untreated eggs (A) and in eggs treated with 100 ^Mcolchicine (D). Of the three fluorescent bodies present in this region of the egg, one correspo
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 122 V. C. ABRAHAM ET AL. Figure 8. Formation of second polar body and pronuclear migration. Untreated eggs (A-C) and eggs treated with 100 colchicine (D-E) were fixed at tn = , subsequently stained with Hoechst 33258, and viewed with either phase contrast (A. D) or epifluorescence (B, C, E) optics. The second polar body (arrowhead) could be seen near the animal pole in both untreated eggs (A) and in eggs treated with 100 ^Mcolchicine (D). Of the three fluorescent bodies present in this region of the egg, one corresponded to the polar body (arrowhead in B, E), and the other two were the male and female pronuclei (C, E). In the untreated egg shown here, the polar body and pronuclei were recorded in separate photographs (B, C) because their focal planes were separated by about 25 jim. The two pronuclei were close to each other and were about 37 ^m from the polar body. In eggs treated with colchicine, the pronuclei were much farther apart (E). Scale bars. A, D. 10 ^m; B, C, E, 50 urn. volvement would seem to require the presence of a unit membrane at the surface of the oil droplets to provide a site of attachment for a kinesin-like molecule. Whether such a membrane is present around these droplets is not known. In other types of cells, unit membranes are present around some lipid droplets but not others (Wake, 1974; Nedergard and Lindberg, 1982). An alternative expla- nation for the effect of these poisons on oil droplet move- ment is that in control eggs a dynamic network of micro- tubules holds the oil droplets in place; in the presence of these microtubule poisons, such a dynamic network would eventually disappear as disassembly continues in the ab- sence of assembly. This question will require further study. The movement of ooplasm toward the animal pole in fish embryos has been previously described as streaming (Roosen-Runge, 1938; Beams et ai. 1985) or bulk How (Gilkey, 1981); our result
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