Two-directional pattern of movements on the cell surface of Amoeba proteus

Particles of latex, glass and precipitated Alcian Blue were studied cinematographically on the surface of migrating Amoeba proteus and in the surrounding medium. The majority of the attached and all unattached particles flow steadily forward in the direction of the endoplasmic streaming and cell locomotion. Flow on the surface is faster than in suspension. Some particles stuck on the membrane move backwards from the frontal region. This retrograde transport is slower than the anterograde flow, and the rate decreases further when the particles approach cell regions adhering to the substratum, accurately following the pattern of the withdrawal of ectoplasm in the same zone. Both movements coexist in the same region and retrograde particles may pass anterograde ones at a distance less than their diameter. Transition from forward flow to backward transport occurs just behind the frontal cap, where the new ectoplasm is formed. The anterograde movement is interpreted as reflecting the general forward flow of the laterally mobile fluid membrane components, which become added to the frontal surface of the locomoting cell; the retrograde movement as retraction of membrane components that, externally, are linked to the transported material and, on the cytoplasmic side, to the contractile microfilamentous layer, as is postulated for cap formation in tissue cells.