  Measurements of the proton structure function $F_2$ in the $Q^2$ range $0.6 -
17 \rm GeV^2$ from ZEUS 1995 shifted vertex data and $Q^2 \simeq 1.5 - 20000
\rm GeV^2$ from 1996 and 1997 ZEUS data are presented. From the former and
other ZEUS $F_2$ data the slopes $d F_2 / d \ln Q^2$ at fixed $x$ and $d F_2 /
d \ln(1/x)$ at fixed $Q^2$ are derived. $F_2$ data at $Q^2$ below $0.9 \rm
GeV^2$ are described successfully by a combination of generalised vector meson
dominance and Regge theory. Using a NLO QCD fit the gluon density in the proton
is extracted in the range $3 \times 10^{-5} < x < 0.7$ from ZEUS 1994 and 1995
data. For $Q^2 \sim 1 \rm GeV^2$ it is found that the $q \bar{q}$ sea
distribution is still rising at small $x$ whereas the gluon distribution id
strongly suppressed. It is shown that these observations may be understood from
the behaviour of the $F_2$ and $d F_2 / d \ln Q^2$ data themselves.
