  This paper is concerned with Devaney chaos in non-autonomous discrete
systems. It is shown that in its definition, the two former conditions, i.e.,
transitivity and density of periodic points, in a set imply the last one, i.e.,
sensitivity, in the case that the set is unbounded, while a similar result
holds under two additional conditions in the other case that the set is
bounded. Furthermore, some chaotic behavior is studied for a class of
non-autonomous systems, each of which is governed by a convergent sequence of
continuous maps.
