The theory of ecological expansion is examined and propositions are developed which suggest that, at advanced stages of metropolitanization, population loss resulting from migration is a function of the decentralization of nonresidential activities from cores to rings coupled with the increased importance of rings as residential centers and the incursion of the residential function into areas beyond the boundaries of the metropolitan community. The changing structure of rings suggests that they are emerging as the hubs of metropolitan activities and that are serving an increasingly central role, integrating cores and areas beyond the boundaries of metropolitan communities as the residential function invades the latter. Although hypotheses are developed to test each of the propositions offered, and although our analysis lends support to the revisions of the theory, the analysis is greatly constrained by the lack of fit between the metropolitan area concept and the census demarcated Standard Metropolitan St...