  Recent ground-based photometric investigations suggest that central regions
of late-type spirals are closely coupled to the inner disk and probably formed
via secular evolution. Evidence presented in support of this model includes the
predominance of exponential bulges, the correlation of bulge and disk scale
lengths, blueness of the bulge and small differences between bulge and central
disk colors, detection of spiral structure into the core, and rapid rotation.
Recent HST observations show that our own bulge and that of M31, M32, and M33
probably harbor both an old and intermediate-age populations in agreement with
models of early collapse of the spheroid plus gas transfer from the disk.
Secular evolution provides a mechanism to build-up central regions in late-type
spirals; mergers or accretion of small satellites could explain the brighter,
kinematically distinct bulges of Sa's and SO's.
