Search

In vitro chondrogenesis is possible in the chick embryo from stage 4 of Hamburger and Hamilton (1951), only 18-19 hours of incubation, before somite formation. In stage 4 of Hamburger and Hamilton (1951) the chondroblasts are placed laterally to the primitive streak and notochord cells are not necessary for cartilage differentiation.

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.

Before the appearance of the morphological primordium of the nervous dissociated, reaggregate selectively "in vitro" and reach high levels of neural differentiation and organization. This property allows the experimental reproduction of the neural differentiation process. Before the appearance of the morphological primordium of the nervous system, its precursory cells carry the necessary information to put in action the basic characteristics of cell differentiation and structural organization, even isolated from the influence of mesoblastic cells.