Mechanisms leading to higher particle concentrations in several places along the meteor stream associated with comet Halley are discussed. The positions of the mass concentrations represented by the mean anomaly of the stream orbit, as determined from long series of observations of the Orionids and Eta Aquarida, are correlated with the deviations in the semi-major axis and nodes of the evolving orbit of the comet. It is shown that random deviations in the orbital elements of the comet may be responsible for the nonstable mass concentrations in the stream.