Have proto-planetary discs formed planets?
  It has recently been noted that many discs around T Tauri stars appear to
comprise only a few Jupiter-masses of gas and dust. Using millimetre surveys of
discs within six local star-formation regions, we confirm this result, and find
that only a few percent of young stars have enough circumstellar material to
build gas giant planets, in standard core accretion models. Since the frequency
of observed exo-planets is greater than this, there is a `missing mass'
problem. As alternatives to simply adjusting the conversion of dust-flux to
disc mass, we investigate three other classes of solution. Migration of planets
could hypothetically sweep up the disc mass reservoir more efficiently, but
trends in multi-planet systems do not support such a model, and theoretical
models suggest that the gas accretion timescale is too short for migration to
sweep the disc. Enhanced inner-disc mass reservoirs are possible, agreeing with
predictions of disc evolution through self-gravity, but not adding to
millimetre dust-flux as the inner disc is optically thick. Finally, the
incidence of massive discs is shown to be higher at the {\it proto}stellar
stages, Classes 0 and I, where discs substantial enough to form planets via
core accretion are abundant enough to match the frequency of exo-planets.
Gravitational instability may also operate in the Class 0 epoch, where half the
objects have potentially unstable discs of $\ga$30 % of the stellar mass.
However, recent calculations indicate that forming gas giants inside 50 AU by
instability is unlikely, even in such massive discs. Overall, the results
presented suggest that the canonically 'proto-planetary' discs of Class II T
Tauri stars {\bf have globally low masses in dust observable at millimetre
wavelengths, and conversion to larger bodies (anywhere from small rocks up to
planetary cores) must already have occurred.}
