They then coalesce by chemotaxis to form an aggregate that becomes surrounded by an extracellular matrix. The aggregate forms a fruiting body, with cells differentiating individually into different components of the final structure.[2] In some species, the whole aggregate may move collectively – forming a structure known as a grex or "slug" – before finally forming a fruiting body. Basic processes of development such as differential cell sorting, pattern formation, stimulus-induced gene expression, and cell-type regulation are common to Dictyostelium and metazoans.