Physico-chemical experiments on the amphibian organizer

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Abstract
A turning-point of the highest importance in the history of embryology was reached when in the spring of 1924 H. Spemann and H. Mangold obtained the first induction by the organizer of an amphibian egg. Th dorsal lip of the blastopore of an embryo of Triton cristatus was transplanted into the indifferent ectoderm of an embryo of Triton taeniatus at the same stage of development, i. e ., the early gastrula. There it did not behave as presumptive medullary plate or epidermis would have done, but on the contrary asserted itself in its new environment by inducing the formation of a new embryonic axis. Two embryos were thus produced on an egg which normally would have formed only one, for the induced structures included neural tube, notochord, auditory vesicles, mesoblastic somites, and Wolffian ducts. Spemann (1921) gave the name "organizer" to cells capable of inducing the formation of new Anlagen , and that of "orgaization-centre" (1918) to the region where such cells are situated during normal development. For this fundamental discovery two main achievements of preparatory investigation had been required. In the first place it had been essential to discover the normal fate of every portion of the amphibian egg and the normal direction of the cell-streams before, during, and after gastrulation. This was accomplished by Vogt (1923, 1925) who stained patches of ectoderm with various dyes and followed the paths taken by the coloured pieces.

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