Evolution of the radius and the internal structure of the star on the birthline without rotation (upper panel) and with rotation (Ω_ini = 2.1 × 10^-5 s^-1, lower panel). In each panel, the upper solid line is the radius and shaded areas correspond to convective regions. The dotted lines indicate the iso-masses. That is, the radius corresponding to fixed values of the lagrangian coordinate M_r (M_r = 1, 2, 3, ... [M_⊙]). Letters along the radius on the upper panel indicate the evolutionary stages described in the text (Sect. 3.1). Numbers along the radius on the lower panel correspond to rotational velocities (in km s^-1) at M = 1, 2, 3, ... [M_⊙].