EVOLUTIONARY STATUS OF WR-TYPE PLANETARY-NEBULA NUCLEI

In this paper we review the evolutionary paths that lead to the differ ent types of planetary nebulae nuclei, including hydrogen and helium-b urning central stars. Starting from the empirical definition of WR cen tral stars, based on stellar spectra, we examine the theoretical work produced to account for the observed configurations. Then we discuss t he constraints provided by recent galactic and extragalactic observati ons, and finally state the possible developments in this field to achi eve a better understanding of the subject.