We study the effect of a massive central singularity on the structure of a triaxial galaxy using N-body simulations. Starting from a single initial model, we grow black holes with various final masses M h and at various rates, ranging from impulsive to adiabatic. In all cases, the galaxy achieves a final shape that is nearly spherical at the center and close to axisymmetric throughout. However, the rate of change of the galaxy's shape depends strongly on the ratio M h /M g of black hole mass to

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... galaxy mass. When M h /M g < ∼ 0.3%, the galaxy evolves in shape on a timescale that exceeds 10 2 orbital periods, or roughly a galaxy lifetime. When M h /M g > ∼ 2%, the galaxy becomes axisymmetric in little more than a crossing time. We propose that the rapid evolution toward axisymmetric shapes that occurs when M h /M g > ∼ 10 −2 provides a negative feedback mechanism which limits the mass of central black holes by cutting off their supply of fuel.