On the histogenetic potency of the tailbud mesoderm.

The caudalmost part of the tailbud mesoderm (terminal paraxial tailbud mesoderm) does not develop into somites. It is not clear whether this terminal paraxial tailbud mesoderm can be considered to be a part of the segmental plate. To elucidate the nature of the tailbud mesoderm, grafts containing caudal somites, caudal prospective somitic mesoderm and the terminal paraxial tailbud mesoderm were grafted from quail embryos into the wing bud mesoderm of chick embryos. The distinct nuclear difference between quail and chick allows the identification of the grafts on a cellular level. The grafts containing caudalmost somites and the prospective somitic mesoderm differentiate into muscle and cartilage. The terminal paraxial tailbud mesoderm, on the other hand, did not give rise to either of these tissues. From this it can be concluded that the terminal paraxial tailbud mesoderm cannot be considered to be a part of the segmental plate.