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We combine new narrow band photometry with archival WFPC2 data for A2218($z$=0.18) and A2125 ($z$=0.25), two clusters with intermediate redshifts butvery different cluster properties, in order to examine the evolution of galaxypopulations. A2218 is a dense, elliptical-rich cluster (Bautz-Morgan type II)similar to Coma in its evolutionary appearance; whereas, A2125 is a less dense,more open cluster (Bautz-Morgan type II-III), although similar in richness toA2218. The color-magnitude relation indicates that A2125 has a more developedblue population than A2218 (the Butcher-Oemler effect), although both clustershave significant numbers of blue galaxies (ranging in star formation rates fromnormal, star-forming disks to starburst systems) as compared to a present-daycluster. The colors of the red populations are identical in A2125 and A2218 andwell fit by passive evolution models. We are able, for the first time, tocombine archived WFPC2 images with our narrow band photometry for a color,morphological and structural analysis of the blue Butcher-Oemler population. Wefind the blue population to composed of two sub-populations, a bright, spiralpopulation and a fainter, dwarf starburst population. A2125 is richer in brightstarburst systems, apparently induced by the cluster's younger dynamical state.In addition, a majority of the S0 population in A2125 and A2218 is composed ofbulge+disk systems, whereas, nearby clusters such as Coma are composedprimarily of lenticulars (pure disk S0's). The structural parameters of the S0bulges in A2125/A2218 are identical to the structure parameters of clusterellipticals suggesting that the disks of some S0's in intermediate redshiftclusters are stripped away with the leftover bulges evolving into present-dayellipticals.Comment: 33 pages AAS LaTeX, 16 figures, accepted for publication in A

Cluster Populations in Abell 2125 and 2218