. The elements of experimental embryology. Embryology, Experimental; Embryology. 406 THE HEREDITARY FACTORS AND DIFFERENTIATION may concern not only such characteristics as pigmentation, but also cell-size, specific growth-intensity, specific structures (see Chap, vi, p. 142 and Chap, vii, p. 236), or the time-relations of development. An example of this last type is provided by experiments in which a portion of presumptive neural tube material of Triton taefiiatus is grafted into the side of an embryo of Triton cristatus. It may there undergo diflPeren- tiation into gills, but such gills pre-
. The elements of experimental embryology. Embryology, Experimental; Embryology. 406 THE HEREDITARY FACTORS AND DIFFERENTIATION may concern not only such characteristics as pigmentation, but also cell-size, specific growth-intensity, specific structures (see Chap, vi, p. 142 and Chap, vii, p. 236), or the time-relations of development. An example of this last type is provided by experiments in which a portion of presumptive neural tube material of Triton taefiiatus is grafted into the side of an embryo of Triton cristatus. It may there undergo diflPeren- tiation into gills, but such gills pre- serve a feature of their specific origin, although the tissues from which they have arisen would normally never have given rise to gills. In Triton taeniatus the gills develop relatively earlier than in cristatus^ and in the experiment just described the gills which are formed from the graft oUaeniatus tissue show Sectorial limb-chrmaera a greater precocity of diflFerentiation axolotl, produced by combining than the host cristatus gills of the other ^^^ ^«^^^! ^^^^ 5^/ hind-limb . ^ . . regeneration-bud irom a black The taeniatus tissue, m its specimen with the ventral half of diflFerentiation into a structure which a hind-limb regeneration-bud 1 , ,1 1 c 1 left in situ on a white speci- It would normally never have formed, ^^^. one year after operation. is still controlled by certain of its (Redrawn after Schaxel, Arch. hereditary factors. Still more demon- ^«^^^^^^^- l, 1922.) strative results have been obtained by xenoplastic grafting between Anura and Urodela (Chap, vi, p. 142). Here, then, is additional evidence of the fact that the hereditary equipment of all the cells of the organism is the same (see Chap, v, p. 85). It is possible to make up a compound embryo by grafting to- gether an anterior half-embryo of Rana virescens and a posterior half-embryo of Rana palustris, or vice versa. The compound organism behaves as a unit in regard to its general physiology a
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