  The current paradigm of star formation through accretion disks, and
magnetohydrodynamically driven gas ejections, predicts the development of
collimated outflows, rather than expansion without any preferential direction.
We present radio continuum observations of the massive protostar W75N(B)-VLA 2,
showing that it is a thermal, collimated ionized wind and that it has evolved
in 18 years from a compact source into an elongated one. This is consistent
with the evolution of the associated expanding water-vapor maser shell, which
changed from a nearly circular morphology, tracing an almost isotropic outflow,
to an elliptical one outlining collimated motions. We model this behavior in
terms of an episodic, short-lived, originally isotropic, ionized wind whose
morphology evolves as it moves within a toroidal density stratification.
