The Spemann's organizer is a region of the amphibian gastrula that will induce a second body axis when transplanted to ventral or lateral regions of a host embryo. The organizer can dorsalise mesoderm, induce convergent extension movements and specify neuroectoderm. Functional equivalents of the Spemann's organizer have been identified in other vertebrates by transplantation experiments. A region of the fish gastrula called the embryonic shield is thought to function as the dorsal organizer. Using a novel surgical method, I showed that the morphological shield can induce complete secondary axes when transplanted into the ventral germ ring of a host embryo. In induced secondary axes, the donor shield contributed to hatching gland, prechordal plate, notochord, floor plate and hypochord. When explanted shields were divided into deep and superficial fragments and separately transplanted, I found that deep tissue can induce ectopic axes with heads but lacking posterior tissues. I found that when only the morphological shield was removed, embryos recovered and were completely normal by 24 hours-post-fertilisation. Ablation of the morphological shield does not remove all goosecoid- and floating head-expressing cells, suggesting that the morphological shield does not comprise the entire organizer region. Removal of the morphological shield plus adjacent marginal tissue, however, led to loss of all shield derivatives, a cyclopean head, loss of floor plate and primary motomeurons and disrupted somite patterning. Embryos from which only the morphological shield was removed still had some goosecoid- and floating head-expressing cells. I have tested whether these residual shield cells were sufficient to form all shield derivatives or, alternatively, if adjacent non-shield tissues could be recruited to shield fate. After morphological shield removal, I found no increase in cell proliferation. Transplantation studies indicated, however, that non-shield tissue may be recruited to a shield fate. Finally, I have employed the shield removal and transplantation method to study two mutations: sneezy and silberblick/wnt11. Transplantation results indicate that sneezy acts autonomously within the shield derivatives. By contrast, silberblick/wnt11 acts non-autonomously in paraxial tissues to drive the convergent extension movement of axial mesoderm.