Cobweb
Cobweb generates hierarchical clustering, where clusters are described probabilistically. Below is an example clustering of the weather data (weather.arff). The class attribute (play) is ignored (using the ignore attributes panel) in order to allow later classes to clusters evaluation. Doing this automatically through the "Classes to clusters" option does not make much sense for hierarchical clustering, because of the large number of clusters. Sometimes we need to evaluate particular clusters or levels in the clustering hierarchy. Below is an approach to doing that.
First see how Weka represents the Cobweb clusters. Below is a copy of the output window, showing the run time information and the structure of the clustering tree.