Action of the rhombencephalon on the differentiation of the auditive placodes. Chronology of its influence.

1. In order to establish the influence of the rhombencephalon on the differentiation of the auditive placode in the embryo of the chicken, and the chronology of this influence, we have extirpated the abovementioned encephalic vesicle in different stages of the embryonic development. We have also carried out transplants of the recently formed auditive vesicle to other embryonic regions. 2. The rhombencephalon is indispensable for the initiation of differentiation of the auditive placode until the pre-somitic phase of the embryonic development. 3. Once the somitic segmentation has begun, the influence of the rhombencephalon is no longer necessary for the formation of the auditive placode, fossa, and vesicle.