An obsession with the chick.

This paper provides a brief account of some aspects of the career of Ruth Bellairs using selected examples from her research publications, with the emphasis being placed on the early stages of chick embryo development, and in particular, on cell migration. Topics include the role of Hensen's node, the vitelline membrane, the structure and segmentation of somites, the tail bud and the Wolffian duct. Her research approach has involved embryo culture, experimental surgery, transmission and scanning electron microscopy, time-lapse filming and immunostaining techniques.