  The Hubble Deep Field images have provided us with a unique chance to relate
statistical properties of high-redshift galaxies to statistical properties of
\lya absorption systems. Combining an {\em empirical} measure of the galaxy
surface density versus redshift with an {\em empirical} measure of the gaseous
extent of galaxies, we predict the number density of \lya absorption systems
that originate in extended gaseous envelopes of galaxies versus redshift. We
show that at least 50% and as much as 100% of observed \lya absorption systems
of $W\apg0.32$ \AA can be explained by extended gaseous envelops of galaxies.
Therefore, we conclude that known galaxies of known gaseous extent must produce
a significant fraction and perhaps all of \lya absorption systems over a large
redshift range.
