. The elements of experimental embryology. Embryology, Experimental; Embryology. 162 prospective fate actually 'obtained reacts by forming a head neural plate I induced head neural plate Induced head. The influence of the host overcomes that of the graft Fig. 78 Diagrams illustrating some of the properties of the organising centre in birds. A, The developmental potencies of a portion of the organiser region are greater than its prospective fate. B, Analysis of the problem presented by the fact that when a piece of the organiser region, the prospective fate of which is trunk mesoderm, is grafte
. The elements of experimental embryology. Embryology, Experimental; Embryology. 162 prospective fate actually 'obtained reacts by forming a head neural plate I induced head neural plate Induced head. The influence of the host overcomes that of the graft Fig. 78 Diagrams illustrating some of the properties of the organising centre in birds. A, The developmental potencies of a portion of the organiser region are greater than its prospective fate. B, Analysis of the problem presented by the fact that when a piece of the organiser region, the prospective fate of which is trunk mesoderm, is grafted into the head region of another blastoderm, it itself gives rise to head mesoderm, while at the same time inducing the formation of neural folds (B i, B 3). The conversion of the graft into head mesoderm may be explained by assuming either: B 2, that after the graft has induced the formation of a head neural plate the latter in turn acts upon the graft and determines it to give rise to head mesoderm; or B 2^, that the conversion of the graft into head mesoderm is due to a process of interaction between the graft and the host's own organising centre, to which latter the property must be ascribed of exerting an influence over an area of given extent, termed an " individuation-field ", in which the whole complex of tissues are controlled in such a way as to lead to the formation of a complete individual. It is, further, an effect of the host's individuation-field that the neural plate which trunk mesoderm induces out of the host-tissues in the head region is head neural plate. That alternative B 2^ is the correct interpretation follows from the cases, C i-C 3, in which the grafted trunk mesoderm in the head region of the host becomes converted into head mesoderm without inducing the formation of a neural plate at all: here, the graft can only be under the in- fluence of the host organising centre. (From Waddington and Schmidt, Arch. Entwmech. cxxviii, 1933.). Please no
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