  We study the properties of evolving wormholes able to exist in a closed
Friedmann dust-filled universe and described by a particular branch of the
well-known Lema{\i}tre-Tolman-Bondi solution to the Einstein equations and its
generalization with a nonzero cosmological constant and an electromagnetic
field. Most of the results are obtained with pure dust solutions. It is shown,
in particular, that the lifetime of wormhole throats is much shorter than that
of the whole wormhole region in the universe (which coincides with the lifetime
of the universe as a whole), and that the density of matter near the boundary
of the wormhole region is a few times smaller than the mean density of matter
in the universe. Explicit examples of wormhole solutions and the corresponding
numerical estimates are presented. The traversability of the wormhole under
study is shown by a numerical analysis of radial null geodesics.
