It was further shown that the neural plate was almost entirely composed of cells from the host taeniatus embryo. Sectioning of the embryo showed that cells from the transplant were incorporated into the mesoderm, the neural plate, and constituted almost the entire notochord of the secondary embryo. This secondary embryo had the normal features of the primary embryo, including structures such as the neural plate and notochord, although they lagged slightly in development. Following this transplant, they observed the formation of a secondary embryonic primordium, consistent with their previous work. A piece from the upper blastopore lip was removed from the cristatus embryo and transplanted into a ventral region of presumptive epidermis in the taeniatus embryo, away from the developing host blastopore. One of the benefits of using the cristatus and taeniatus embryos was that the cristatus embryo cells lacked pigment so the fate of the transplant could be easily tracked when placed among the pigmented taeniatus cells. The experiment performed resembled the one done in 1918, however instead of a homoplastic transplantation they used embryos from two species of newt that are closely related. To test this hypothesis, Spemann, along with Hilde Mangold, performed experiments between 19 using embryos from Triturus cristatus and Triturus taeniatus that were undergoing gastrulation. This work provided the initial evidence to support the notion that there existed some “organization center” that was determined prior to the other embryonic tissue and influenced the determination of surrounding cells. He also fused together two identical halves from different embryos and observed formation of the neural plate. Additionally, splitting the embryo in half and rotating the animal pole in respect to the vegetal pole resulted in determination spreading from the lower vegetal pole, where the upper blastopore lip was located, to the upper animal half. Spemann also showed that by transplanting a piece from the upper blastopore lip into an area of presumptive epidermis, a secondary embryonic primordium formed, including a secondary neural tube, notochord and somites. In 19, Hans Spemann showed that transplanting presumptive epidermis into the area of presumptive neural tissue would change the fate of the transplanted cells to that of their new destination, and likewise when he transplanted presumptive neural tissue to where the presumptive epidermis was forming. Prior to its discovery, it had been hypothesized by multiple groups that there exists a portion of the developing embryo that serves as an "organization center". The Spemann-Mangold organizer was first described in 1924 by Hans Spemann and Hilde Mangold.
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