Evolution of the surface hydrogen abundance (in mass fraction) for 40 M_⊙ models. The limit for becoming a WR star (X_s< 0.3) is indicated with a gray dotted line. The models plotted are the same as those presented in Figs. 1 and 2. Left panel: cases of spin down. The Z = 0.014 and Z = 0.002 models have initial rotation on the ZAMS equal to 365 km s^-1 and 391−394 km s^-1, respectively (see Table. 1)). Right panel: cases of spin up. The Z = 0.014 and Z = 0.002 models have initial rotation on the ZAMS equal to 151 km s^-1 and 163-167 km s^-1, respectively.