One of the ways in which Fundulus deep cells move in vivo is by putting out long, fingerlike protrusions. This involves a change in the shape of the cell as a whole, with cytoplasmic flow, and is not just a local phenomenon. Moreover, particles on the cell surface move toward a protrusion as it is forming, suggesting surface flow. The role of surface flow is discussed both on a grown level and in respect to molecular fluidity. Long, stable protrusions can be pulled from cells by the application of negative pressure at a constant rate and these behave in a similar way to those formed during cell locomotion. Such long protrusions must be structured. The importance of contractile properties of the cytoplasm in the formation of protrusions was studied by treating cells with media that modify cellular contractility.

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