Final answer:
The statement that cells aggregate after migration to form structures is true, as exemplified by the behavior of the cellular slime mold Dictyostelium and during embryogenesis, where cells move to aggregate, differentiate, and form multicellular structures.
Step-by-step explanation:
The statement that cells, once they migrate, aggregate with other cells to form structures is true. This process is evident in various biological contexts, such as the development of multicellular organisms, tissue differentiation, and the behavior of certain uni- and multicellular organisms. For instance, in the aggregation stage of cellular slime molds like Dictyostelium, individual cells respond to chemical signals and move toward a gathering point, where they aggregate and eventually form a slug-like structure. This aggregation implies that cells coordinate and communicate extensively, underpinning the development of distinct three-dimensional forms. Additionally, during embryogenesis, cells migrate and form attachments to the extracellular matrix via an interplay of integrins and substances like fibronectin, which further guides cell and tissue differentiation. The aggregation and coordination of cells are crucial steps that contribute to the proper organization and function of multicellular organisms.