  We present results of new photoionization calculations for investigating
gaseous regions that represent potentially expected stages of nuclear
processing in the Crab Nebula supernova remnant. In addition to gas resulting
from CNO-processing and oxygen-burning, as previously reported, a large
component of the nebula appears to be carbon-rich. These results suggest that
the precursor star had an initial mass of 9.5 solar masses or more.
