  We provide observational and theoretical perspectives on the currently much
debated issue of the Fanaroff-Riley (FR) morphological dichotomy of
extragalactic radio sources. In this context we introduce a new, albeit rare,
class of double radio sources in which the two lobes exhibit clearly different
FR morphologies. It is argued that such `HYbrid MOrphology Radio Sources', or
HYMORS, could be used to effectively constrain the theoretical mechanisms
proposed for the FR dichotomy. Basically, the existence of HYMORS supports
explanations for the FR dichotomy based upon jet interaction with the medium
external to the central engine, and appears quite difficult to reconcile with
the class of explanations that posit fundamental differences in the central
engine, such as black hole spin or jet composition, to be responsible for the
two FR classes of double radio sources.
