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The morphological classification of BCM's, when augmented with quantitative surface photometry, leads to the conclusion that BCM's are special objects, beyond being mere extrapolations of the luminosity function. Morphology paved the way for an examination of these objects and has led to an interpretation of their properties within the context of dynamical evolution, mergers and cannibalism. When the structural information is combined with kinematics of the underlying galaxies, dynamics of cluster cores and color information about the component stellar populations, we are persuaded that the evolution of BCM's has two primary elements. The first is that the interior properties of BCM's are determined by a long history of hierarchical merging (i.e. the cannibalism of smaller cluster members). The "diffuseness" of BCM's and their enlarged characteristic radii are all signatures of past mergers. These conclusions define the class of D galaxies and are drawn from parameters that are independent of the cD envelopes found around some BCM's. The second process in the evolution of BCM's is the occurrence of cD envelopes, a feature in BCM's which is invisible to the eye and, thus, morphological classification. All evidence points to the origin of cD envelopes as primordial, before cluster collapse, at the same epoch of star formation that produced the populations in galaxies. Whether all galaxies had cD envelopes to be later stripped off by the cluster mean tidal field, or whether they developed from stripping other cluster members in local subgroups before cluster collapse, remains unknown.