ABSTRACT
Aggregation is the gathering together of units to make a larger unit. The resultant larger unit is also called an aggregation. With that in mind and with the unabashed assumption that aggregation is a fundamental condition, function, and structure in biology, we shall define "cell aggregation" as the gathering together of cells to form fairly stable, contiguous, multicellular associations under physiological conditions. The definition contains two principal elements: physical movement and stable multicellular contacts. Both need to be present in any cell aggregation system. The following criteria are derived from the definition and the enumerated exclusions. To be included in a list of cell aggregation phenomena, a system must be active, inducible, stable, suspension, intercellular, multicomponent and spontaneous. H. Hoffman in 1964 treated bacterial aggregations as models of morphogenesis. His concept of aggregation, however, remains exactly that, that which we have dismissed as purely conceptual.
