EGG CORTEX IN MORPHOGENESIS
379
FIG. 10. Experiments of Curtis in Xenopus. (a) Excision of the cortical grey crescent
area at the one-cell stage: no gastrulation. (6) Same experiment at the 8-cell stage:
normal embryo, (c) Graft of the grey-crescent cortex of the one-cell stage to the ventral
part of the 8-cell stage does not result in the induction of a secondary embryonic axis.
(d) Graft of the grey-crescent cortex from the 8-cell stage to the ventral margin of the
one-cell stage induces a secondary embryonic axis. (After Curtis, 1962, but order of
figures modified.)
That such an evolution must occur, through an interaction of cortical
field and inner yolk material, was foreseen by the theory of Dalcq and
Pasteels (1937, 1938b) although we were not able to state at what stage
this would happen. By his experiment Curtis has shown that a fundamental morphogenetic event, which promotes gastrulation and forma-
379
FIG. 10. Experiments of Curtis in Xenopus. (a) Excision of the cortical grey crescent
area at the one-cell stage: no gastrulation. (6) Same experiment at the 8-cell stage:
normal embryo, (c) Graft of the grey-crescent cortex of the one-cell stage to the ventral
part of the 8-cell stage does not result in the induction of a secondary embryonic axis.
(d) Graft of the grey-crescent cortex from the 8-cell stage to the ventral margin of the
one-cell stage induces a secondary embryonic axis. (After Curtis, 1962, but order of
figures modified.)
That such an evolution must occur, through an interaction of cortical
field and inner yolk material, was foreseen by the theory of Dalcq and
Pasteels (1937, 1938b) although we were not able to state at what stage
this would happen. By his experiment Curtis has shown that a fundamental morphogenetic event, which promotes gastrulation and forma-