  We calculate a grid of star models with and without the effects of axial
rotation for stars in the mass range between 2 and 60 M$_{\odot}$ for the
metallicity $Z = 10^{-5}$. Star models with initial masses superior or equal to
9 M$_\odot$ were computed up to the end of the carbon--burning phase. Star
models with masses between 2 and 7 M$_\odot$ were evolved beyond the end of the
He--burning phase through a few thermal pulses during the AGB phase. Compared
to models at $Z=0.02$, the low $Z$ models show faster rotating cores and
stronger internal $\Omega$--gradients, which favour an important mixing of the
chemical elements. In very low $Z$ models, primary nitrogen is produced during
the He--burning phase by rotational diffusion of $^{12}$C into the H--burning
shell. The intermediate mass stars of very low $Z$ are the main producers of
primary $^{14}$N, but massive stars also contribute to this production; no
significant primary nitrogen is made in models at metallicity $Z$=0.004 or
above. We calculate the chemical yields in He, C, N, O and heavy elements and
discuss the chemical evolution of the CNO elements at very low Z. Remarkably,
the C/O vs O/H diagram is mainly sensitive to the interval of stellar masses,
while the N/O vs O/H diagram is mainly sensitive to the average rotation of the
stars contributing to the element synthesis. The presently available
observations in these diagrams seem to favour contributions either from stars
down to about 2 M$_{\odot}$ with normal rotation velocities or from stars above
8 M$_{\odot}$ but with very fast rotation.
