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Lutz had done in ovo, by means of a technique of microsurgery. The
results of the two authors correspond closely with regard to the regulatory power of all parts of the area pellucida, and to the fact that no
part of the area opaca is capable of forming an embryo. All territories
of the area pellucida are embryonic, provided that they contain a
sufficiently large number of cells. The blastoderms were cut either into
two equal parts following the plane of bilateral symmetry, or perpendicularly to that plane; or into four equal sections; or finally into two or
four unequal sections. In most cases, an embryo could be formed in
each isolated fragment. The same thing is true if the area pellucida is
sectioned into lateral or median parts.
It seems that, in incubated eggs until the stage of the beginning of
the primitive streak, regulatory power tends to be limited to the posFIG. 16. Diagrammatic summary of the frequency of development of embryonic axial
systems in various types of isolates, d, Incubated pre-streak stage; e, initial and intermediate
streak stages; remainder all unincubated blastoderms. (After Spratt and Haas, 1960c.)