have used Renzini and Voli’s (1981) nucleosynthesis calculations for a value of the mass loss parameter $\eta$ = 0.33 (Reimers 1975), and mixing length $\alpha_{RV}$ = 1.5. The standard value for M$_{up}$ is 8 M$_{\odot}$.

b\) For massive stars (M $>$ 8 M$_{\odot}$) we have used Woosley’s (1987) nucleosynthesis computations but adopting the relationship between the initial mass $M$ and the He-core mass M$_{He}$, from Maeder and Meynet (1989). It is worth noting that the adopted M(M$_{He}$) relationship does not substantially differ from the original relationship given by Arnett (1978) and from the new one by Maeder (1992) based on models with overshooting and Z=0.001. These new models show instead a very different behaviour of M(M$_{He}$) for stars more massive than 25 M$_{\odot}$ and Z=0.02, but the galaxies we are modelling never reach such a high metallicity.

c\) For the explosive nucleosynthesis products, we have adopted the prescriptions by Nomoto et al. (1984), model W7, for type Ia SNe, which we assume to originate from C-O white dwarfs in binary systems (see Marconi et al. (1994) for details). More recent nucleosynthesis calculation by Thielemann et al. (1993) do not significantly differ from the Nomoto et al. (1984) ones.

The nucleosynthesis 