A consideration of the extraneous coats of the plasma membrane.

This review is concerned with the role of the "extraneous coat" of the ameba in pinocytosis. It also considers the possible role of the extraneous coat as an additional barrier to those exchanges betvw een the cytoplasm and the environment which involve diffusion. Several examples of pinocytosis in mammalian tissues are presented and are appraised with respect to the physical-chemical properties of the extraneous coat. Types of transport that dlo not appear to operate by way of pinocytosis are similarly considered.