The Hierarchy Browser only graphs relations a defined number of levels away from the root node (starting term). The default setting is 4, but can be changed by the "Number of Levels" menu. The available settings are NONE, 1-9 and ALL for both height and depth.
Try graphs using these parameters and different settings of "Number of Levels":
Index Argument: 2 Starting Term: Animal Microtheory: BaseKB Binary Predicate: genls
The Hierarchy Browser indicates if there are more nodes beyond the maximum depth or if a node is a leaf on the hierarchy tree. The symbol used for both of these situations can be selected on the "Hierarchy Browser Colors and Symbols" page reachable from this page.