. The elements of experimental embryology. Embryology, Experimental; Embryology. 158 organisers: inducers of differentiation organiser-invagination) either diverge or converge anteriorly.^ In the former case, the compound embryo will have a Y-shaped primitive gut-roof with the divergence anterior, and will develop double heads; in the latter case the divergence will be posterior, and there will be double hind ends. Perhaps the most remarkable cases of teratological development induced experimentally are those producing crossed doubling Herz. Med. Herz Fig. 76 Transverse section through a dupli
. The elements of experimental embryology. Embryology, Experimental; Embryology. 158 organisers: inducers of differentiation organiser-invagination) either diverge or converge anteriorly.^ In the former case, the compound embryo will have a Y-shaped primitive gut-roof with the divergence anterior, and will develop double heads; in the latter case the divergence will be posterior, and there will be double hind ends. Perhaps the most remarkable cases of teratological development induced experimentally are those producing crossed doubling Herz. Med. Herz Fig. 76 Transverse section through a duplicitas cruciata embryo of Triton, such as that shown in fig. 75. The hearts {Herz) are formed partly from each embryonic rudiment, and are therefore situated laterally. Med., neural tube. (From Wessel, Arch. Entwmech. cvii, 1926.) (duplicitas cruciata). These result from the grafting together of two gastrula halves each containing the dorsal lip, in such a way that the directions of organiser-invagination are directly opposed to one another. Invagination takes place in each half, and the primitive gut-roofs meet one another, head on. Being unable to make any further progress forwards, they move to each side. The result is that the primitive gut-roofs together form a cross, two (opposite) branches of which are formed each from one of the two invagina- tions, and the other two branches are composite, half of each being ^ Spemann, 1916, 1918; Koether, Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Huxley, Julian, 1887-1975; De Beer, Gavin, Sir, 1899-1972. New York [Hafner Pub. Co. ]
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