  In this talk I first briefly explain the puzzle presented by the high muon
content observed in air-showers which point to the ultra high-energy $\gamma$
sources like the HER-X-1. Since it had been suggested that a possible
explanation of the puzzle might come from the effects of the hadronic structure
of the photon, I briefly explain the concept of photon structure function and
comment on the uncertainties in the predictions of the \sigtot. Then I show
that while the current experiments at the \eplem\ (TRISTAN and LEP) and $ep$
(HERA) colliders have seen clear evidence for the hadronic structure of the
photon, the observed muon excess in the air shower experiments, if confirmed by
other experiments to be at the same high level, can not be explained in terms
of the photon structure function.
