[en] Suggestions for further work on the classification of Wolf-Rayet stars are made, especially in relation with the anomalies presented by certain nuclei of planetary nebulae. In the Of-stars, in which the spectra are superpositions of typical observations O-stars and shell lines, remarkable differences occur in the relative intensities of various shell lines. The relations between X-and Of-stars are discussed. The peculiar intensities presented by certain transitions of various atoms in anomalous stars of early type are examined. The physical factors (dilution, fluorescence, departure from black body distribution, chemical composition) affecting the relative intensities of various transitions within one atom, and of various atoms relative to each other, are discussed.