The effects of Janus Green B on the temporal and spatial pattern of feather germ morphogenesis

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Abstract
The normal timing and appearance of feather germs was per‐turbed by injecting the dye Janus Green B into the amniotic fluid of chick embryos at late stage 28, prior to the first appearance of feather germs. This treatment prevented feather germ morphogenesis in some regions while else‐where it delayed normal morphological development. The Janus Green B effect lasted for approximately 98 hours. Feather regions, which normally form epidermal placodes during the period of treatment, showed the longest delays in subsequent feather germ formation and were the most likely to remain featherless. These results suggest that the epidermal placode stage is critical for feather germ formation. Janus Green B appears to prevent feather germ morphogenesis by interfering with development prior to this critical stage. Since severely affected regions fail to recover their capacity to form feather germs, even after the period of sensitivity to the dye, a limited period of competence is suggested for feather germ formation.