As time proceeds, the stripes propagate. Here and . Plainly, spirals rotate. Spirals are also extremely stable. The two rings annihilate each other where they meet.
New rings originate from the two centers.
1 b and 2 b. Here and . There may be several centers generating new rings all the time. These propagate outwards. If two nonconcentric rings hit each other, they annihilate their common part while moving outwards.