  We use archived IRAC images from the Spitzer Space Telescope to show that
many Class 0 protostars exhibit complex, irregular, and non-axisymmetric
structure within their dusty envelopes. Our 8 $\mu$m extinction maps probe some
of the densest regions in these protostellar envelopes. Many of the systems are
observed to have highly irregular and non-axisymmetric morphologies on scales
>= 1000 AU, with a quarter of the sample exhibiting filamentary or flattened
dense structures. Complex envelope structure is observed in regions spatially
distinct from outflow cavities, and the densest structures often show no
systematic alignment perpendicular to the cavities. These results indicate that
mass ejection is not responsible for much of the irregular morphologies we
detect; rather, we suggest that the observed envelope complexity is mostly the
result of collapse from protostellar cores with initially non-equilibrium
structures. The striking non-axisymmetry in many envelopes could provide
favorable conditions for the formation of binary systems. We also note that
protostars in the sample appear to be formed preferentially near the edges of
clouds or bends in filaments, suggesting formation by gravitational focusing.
