Variable N galaxies as composite systems

Procedures are developed on the basis of Sandage's composite N galaxy model for interpreting the trajectories traced out by variable N galaxies in the color-color diagram. These procedures are shown to give reasonable results when applied to published data for the N galaxies 3C 390.3 and PKS 0321-36. The same procedures are then applied to published data for the peculiar variable BL Lac. The lack of observable spectral features is still unexplained. Otherwise, the results are consistent with the identification of BL Lac as a composite N galaxy at z 0.022. Subject heading: galaxies, photometry of