In the light of present knowledge on stellar evolution, it is shown that red ZAHB will not develop for very low metal globular clusters if Y is appreciably greater than 0.1. Recent determinations of the mass-sizes of the Re- cores at the time of the He-flash support independently conclusion that, if no increase in surface He-abundanice occurs between the turn-off evolutionary phase and the 13.B. stages, Y-values lower than 0.2 imply ages of the clusters larger than 20 b.y. By comparing evolutionary paths with the observed populations of the horizontal branches evidence is found for mass loss in blue H.B., and evidence for mass dispersion in red H.B. not depopulated in RR Lyrae. A few clusters (M3, M15) have their H.B. dominated by mass dispersion. Finally the expected correlations between mass loss and spatial distribution of H.B. stars are briely discussed in order to point out sone observational possibilities. (auth)