. The elements of experimental embryology. Embryology, Experimental; Embryology. 274 FIELDS AND GRADIENTS undetermined as to be able to produce any structures, internal or external. On pushing analysis further, it is found that the original control of differentiation in all cases appears to be exerted in relation to what may be called a biological or morphogenetic field. Within these. Fig. 129 Gradients of various kinds in the earthworm Pheretima. O O and outer left-hand scale, oxidisable substance as determined by the Manoilov reaction. X X and outer right-hand scale, solid content, per cent.
. The elements of experimental embryology. Embryology, Experimental; Embryology. 274 FIELDS AND GRADIENTS undetermined as to be able to produce any structures, internal or external. On pushing analysis further, it is found that the original control of differentiation in all cases appears to be exerted in relation to what may be called a biological or morphogenetic field. Within these. Fig. 129 Gradients of various kinds in the earthworm Pheretima. O O and outer left-hand scale, oxidisable substance as determined by the Manoilov reaction. X X and outer right-hand scale, solid content, per cent. V V and inner left-hand scale, temperature at which heat-shortening occurs. • ©and inner right-hand scale, electrical potential, millivolts. (Redrawn after Watanabe, Set. Rep. Tohokii Imp. Univ. vi, 1931.) fields, various processes concerned with morphogenesis appear to be quantitatively graded, so that the most suitable name for them is field-gradient systems, or simply gradient-fields.^ ^ Historically, concepts of this type were first introduced into embryology by Boveri (1901, 1910); later Child (1915 a) generalised a large number of observa- tions in the form of his theory of axial gradients; the term field, however, was only introduced in the last few years, notably by Spemann ("Organisationsfeld") (1921), Gurwitsch (1922, 1927), Weiss (1927 c), Bertalanffy (1928), de Beer (1927).. 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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