. The elements of experimental embryology. Embryology, Experimental; Embryology. 272 FIELDS AND GRADIENTS limb grafted on to the base of a tail actually produces a little super- numerary tail (fig. 127). The undetermined stage of the regeneration-bud is of limited duration. Whereas a bud of hemispherical form is still undeter- mined, by the time a markedly conical shape has been attained, the bud is determined, and if grafted elsewhere will now continue to differentiate in accordance with its place of origin instead of in accordance with its new situation. In this respect regenerated tissue be
. The elements of experimental embryology. Embryology, Experimental; Embryology. 272 FIELDS AND GRADIENTS limb grafted on to the base of a tail actually produces a little super- numerary tail (fig. 127). The undetermined stage of the regeneration-bud is of limited duration. Whereas a bud of hemispherical form is still undeter- mined, by the time a markedly conical shape has been attained, the bud is determined, and if grafted elsewhere will now continue to differentiate in accordance with its place of origin instead of in accordance with its new situation. In this respect regenerated tissue behaves just as do the various regions of the amphibian egg, which also pass from a plastic to a determined phase.^. Fig. 127 Lack of determination in early regeneration-buds. Triton larva showing a tail (against a square of white paper) developed from an early limb regeneration-bud grafted into the tail-field. (From Guy^not, Rev. Suisse de Zool. xxxiv, 1927.) The success of the converse experiment in which the early re- generation-bud of a tail is grafted on to the stump of an amputated hind-limb, or into the fore-limb field, close to the base of the (un- operated) host-limb, and then produces a limb,^ has also been reported, but this, though highly probable, cannot be regarded as conclusively proved^ (fig. 128). ^ Guy^not, 1927; Guyenot and Ponse, 1930. " Weiss, 1927 B. â ^ The experiment was done with regeneration-bud and host belonging to the same species, and it is difficult therefore to be absolutely certain that the limb developed from the grafted cells. Further, as pointed out by Guyenot, the graft may have come under the influence of the endings of the brachial nerve, which are known to be able to produce the formation of a limb (see p. 362). However, the presumption is that Weiss' interpretation is Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of thes
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