![]() This latter process was initially called the primary embryonic induction and is now more properly called neural induction.Ī certain degree of regional differences among induced neural structures had already been observed by Spemann himself: some of them represented more cranial derivatives of CNS, others were more caudal ones. The formation of a neural plate which gives rise to the central nervous system (CNS) was considered to be a result of an inductive influence from the underlying mesoderm (organizer property). Today researchers usually call it the Spemann's organizer. The dorsal lip, the influence of which causes the development of a new embryo, had been termed the organizer. The participation of a dorsal blastopore lip in the programme of development of a new embryo may be regarded in three significant aspects: 1/Formation of axial structures and establishment of the plane of bilateral symmetry 2/Redetermination of fate for the party of host cells and their inclusion in the structures induced by the transplant 3/Induction of the nervous system. In another experiment, when the transplant was taken from a lightly pigmented embryo of Triturus cristatus and transferred to a heavily of pigmented Triturus vulgaris, it was shown that the secondary neural structures originated mainly from cells of the recipient. As a result, a secondary complex of axial organs including head structures was formed at the place of a transplant. Recent studies into the history of this discovery ( Sander, 1993) have detected that the decisive experiment had been made by Hilda Mangold in 1921 when she transplanted a piece of dorsal lip of the ring-like blastopore of a Triturus embryo to the ventral side of another embryo at the same stage. They had observed that after transplantation of a dorsal blastopore lip of the early gastrula to the ventral side of another embryo a secondary embryonic axis developed on this side. Mangold discovered the so-called “organizer” in amphibian embryos ( Spemann and Mangold, 1924). Sometimes it seems that to the end of XX century the embryologists are further from the original goal to explain how the development of an organism is accomplished than it seemed at the beginning of the century when H. Up to now researches are far from understanding fully the mechanisms which realize the embryonic development of vertebrate animals. The researches of many commentators have already thrown much darkness on the subject, and it is probable that, if they continue, we shall soon know nothing at all about it.
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