Silkie the "SHH" gene, called the ZPA Regulatory Sequence (ZRS). This causes ectopic "SHH" expression in the anterior of the developing limb bud, leading to increased tissue growth and digits. While the feet of the Silkie display polydactyly, the wings have the standard tridactyly (three digit) arrangement. The Japanese Silkie initially develops additional digits in the wing as an embryo, but these are lost prior to hatching. The genetic cause behind Silkie polydactyly differs from those that cause polydactyly in the Dorking chicken breed, which is due to ectopic "FGF4" expression in the AER, with ectopic "SHH" a secondary effect. The
A Bird came down the Walk other evil forces.Then the narrator offers the bird a piece of crumb,but the bird neglects it and then it flies away. Helen Vendler regards the poem as a "bizarre little narrative" but one that typifies many of Dickinson's best qualities. She likens the poet to a reporter observing a murderer in the act, and later, pretending fear that the murderer may be dangerous to herself and must be mollified by a "crumb". The bird takes flight and Vendler regards what follows - the description of the bird in flight - as "the astonishing part of the poem". Vendler notes that