  The effects of resonances and flow on the correlation function for two
identical particles are described assuming chaotic sources and classical
propagation of particles. Expanding to second order in relative momenta, the
source sizes can be calculated directly and understood as contributions from
various fluctuations in the source. Specific calculations of source size radii
are given assuming Bjorken longitudinal flow with additional transverse
expansion. Results are compared to recent $\pi\pi$ and $KK$ correlation data
from relativistic nuclear collisions with particular attention to the reduction
in the $\pi\pi$ correlation function due to resonances and the decreasing
source sizes with increasing transverse momenta of the particles.
