Starting with genes which constitute the most basic level, transposons may belong to a meta-level in the sense that they represent instructions for genes. In short, the nucleus, far from being a 'dumb' library of the intelligent cell, is clearly an intelligent system in its own rights. The 'skin' of the cell that transmits materials and sensory signals beween the inside of the cell and its outside world. A biological 'cloud chamber' that allows cells to record their own movements in the form of tracks that they leave in a carpet of tiny gold particles on the substrate. A motile and ephemeral surface projection out of the cortex of a cell.
Examples are filopodia, lamellipodia and blebs.
A lamellipodium in the process of folding back onto the cell body from which it extended earlier. Seen from the side, ruffles are straight like pencils that swivel around one end near the substrate. Seen from above, the opposite ends of many such 'pencils' which point freely into the culture medium form a wavy outline. The basic movement is shown schematically below in the case of a hypothetical lamellipodium that surrounds the entire cell. Both front and tail of a migrating cell are expressions of its so-called polarity.