Feather array formation with and without a global wave.

(A) In the in vitro reconstituting chicken skin explant, the morphogenetic field (blue) is experimentally static, leading to the simultaneous formation of a less ordered feather (red circle) array. (B) In flightless birds, this less ordered feather array is formed because it is based only on the Turing patterning principles in a local static morphogenetic field. (C) In in vivo flight birds, the high ordered feather array is formed sequentially from the midline to lateral regions by the morphogenetic waves that travel bilaterally.