  Recent observations of GRS 1915+105 and GRO J1655+40 reveal superluminal
motions in Galactic sources. This letter examines the physical conditions
within these Galactic sources, their interaction with their environment, their
possible formation, and contrasts them with their extragalactic counterparts.
In particular, e$^{+}$-e$^{-}$ and e-p jets are contrasted, constraints on
particle acceleration in the jets are imposed using X-ray and radio
observations, the $\gamma$-ray flux from e$^+$-e$^-$ jets expected at EGRET
energies and the flux in infrared lines from an e-p jet are estimated. It is
also suggested that these sources may exhibit low frequency radio lobes
extending up to several hundred parsecs in size, strong, soft X-ray absorption
during the birth of the radio components and emission line strengths
anti-correlated with the X-ray flux. The implications for other X-ray
transients are briefly discussed.
