The mechanism of movement demonstrated by Amoeba spp. and other cells that are capable of changing their shape (e.g. phagocytes). The cytoplasm of Amoeba spp. consists of a central fluid plasmasol surrounded by a more viscous plasmagel. The plasmagel is converted to plasmasol, which slides towards the front of the cell, forming a pseudopodium and propelling the cell forward. On reaching the tip of the pseudopodium, this plasmasol is reconverted into plasmagel; at the same time the plasmagel at the rear of the cell is converted into plasmasol and streams forward, thus maintaining continuous movement.

Amoeboid movement is brought about by reversible changes in the actin filaments of the cell’s cytoskeleton. Cross-linking of these filaments by other proteins creates a three-dimensional network with gel-like properties in the plasmagel region. Disassembly of this network causes reversion to the sol state of plasmasol.