  The fraction of star-forming galaxies in rich clusters of galaxies increases
rapidly with the redshift. This is interpreted as the result of a rapid
evolution of cluster galaxies, though its mechanism is not yet clear. One
hypothesis is that if galaxies run into the dense intracluster medium (ICM)
regions, starbursts can be induced due to compression of molecular clouds in
the galaxies by a raised "external" ICM pressure. In a merging cluster, there
would be dense ICM regions and some galaxies may experience a rapid increase of
external pressure. Thus, if the mechanism works, starbursts would occur in such
galaxies. Such a situation is considered to be realized in Coma cluster, and
galaxies showing a recent starburst have a characteristic spatial distribution;
they populate an elongated region between two sub-clusters. We examined the
above hypothesis by measuring the spatial distribution of blue galaxies,
regarded as star-forming galaxies in Abell~168 to check whether a case like
Coma is realized in this recently merging cluster. However, we could not find
an enhanced blue-galaxy distribution between two sub-clusters. We discuss the
causes of our result, including possibilities of surviving the hypothesis.
