Mirages in galaxy scaling relations
  We analyzed several basic correlations between structural parameters of
galaxies. The data were taken from various samples in different passbands which
are available in the literature. We discuss disc scaling relations as well as
some debatable issues concerning the so-called Photometric Plane for bulges and
elliptical galaxies in different forms and various versions of the famous
Kormendy relation.
  We show that some of the correlations under discussion are artificial
(self-correlations), while others truly reveal some new essential details of
the structural properties of galaxies. Our main results are as follows:
  (1) At present, we can not conclude that faint stellar discs are, on average,
more thin than discs in high surface brightness galaxies. The ``central surface
brightness -- thickness'' correlation appears only as a consequence of the
transparent exponential disc model to describe real galaxy discs.
  (2) The Photometric Plane appears to have no independent physical sense.
Various forms of this plane are merely sophisticated versions of the Kormendy
relation or of the self-relation involving the central surface brightness of a
bulge/elliptical galaxy and the Sersic index n.
  (3) The Kormendy relation is a physical correlation presumably reflecting the
difference in the origin of bright and faint ellipticals and bulges.
  We present arguments that involve creating artificial samples to prove our
main idea.
