384
JEAN J. PASTEELS
Modifications of this gradient may be found (see Dollander et al.) in
eggs in which the vegetal yolk was displaced by the effect of gravity
(partial or total rotation in a fixed position, or centrifugation) ; and
there is always a close agreement between the increase of permeability
(estimated by the depth of dye penetration) and the morphogenetic
effects. The area where a dorsal blastopore lip will appear has always an
increased permeability. This is true, for instance for Born's crescent.
We have already seen in our own experimental results, that the
competition between grey-crescent factor and Born's crescent implies
some change (but not an entire remodelling) of the pattern of the
cortical field.
The results of Dollander's team tend to show that this modification
might be linked to permeability. Of course, these studies of dye
penetration merely give a hint as to the nature of the physiological
activities involved. Further work is required to demonstrate : (1) whether
those differences in permeability to the dyes correspond to general
differences in permeability concerning all diffusible factors ; (2) how an
increase of permeability in the dorsal part of the cortex might increase
the morphogenetic potential.
The same trend of ideas has lead Lovtrup (1958) to an interesting
hypothesis : that the 'dorsal' aspect of the egg is determined by conditions which allow a greater aerobic metabolism. In other words, that
the morphogenetic potential should be parallel to the rate of oxygen
consumption which would depend on differences in cortical permeability.
Lovtrup and Pigon (1958) have tried to give an experimental demonstration of this interesting hypothesis. They have partially deprived
eggs of the axolotl at the 2-cell stage of oxygen by placing them with
one side in close contact with glass and allowing the other side to remain
free. In most cases the dorsal lip of the blastopore appeared at the
oxygenated side. Unfortunately the experimental conditions were too
imprecise to permit clear-cut conclusions to be made : no attention was
paid to the localization of the clear crescent. More recently permeability
to water has been considered by L0vtrup (1962b), but it concerns only
the egg as a whole.
VIII. Structural Organization of the Cortex
The structure of the cortex has been investigated by Dollander (1954,
1955, 1956, see also 1962) who used several techniques including the
electron microscope. A more refined electron microscopical technique
was recently used by Wartenberg and Schmidt (1960). There is good
agreement between both series of observations. Peculiar changes arise
after fertilization, but in different directions according to the taxonomic
JEAN J. PASTEELS
Modifications of this gradient may be found (see Dollander et al.) in
eggs in which the vegetal yolk was displaced by the effect of gravity
(partial or total rotation in a fixed position, or centrifugation) ; and
there is always a close agreement between the increase of permeability
(estimated by the depth of dye penetration) and the morphogenetic
effects. The area where a dorsal blastopore lip will appear has always an
increased permeability. This is true, for instance for Born's crescent.
We have already seen in our own experimental results, that the
competition between grey-crescent factor and Born's crescent implies
some change (but not an entire remodelling) of the pattern of the
cortical field.
The results of Dollander's team tend to show that this modification
might be linked to permeability. Of course, these studies of dye
penetration merely give a hint as to the nature of the physiological
activities involved. Further work is required to demonstrate : (1) whether
those differences in permeability to the dyes correspond to general
differences in permeability concerning all diffusible factors ; (2) how an
increase of permeability in the dorsal part of the cortex might increase
the morphogenetic potential.
The same trend of ideas has lead Lovtrup (1958) to an interesting
hypothesis : that the 'dorsal' aspect of the egg is determined by conditions which allow a greater aerobic metabolism. In other words, that
the morphogenetic potential should be parallel to the rate of oxygen
consumption which would depend on differences in cortical permeability.
Lovtrup and Pigon (1958) have tried to give an experimental demonstration of this interesting hypothesis. They have partially deprived
eggs of the axolotl at the 2-cell stage of oxygen by placing them with
one side in close contact with glass and allowing the other side to remain
free. In most cases the dorsal lip of the blastopore appeared at the
oxygenated side. Unfortunately the experimental conditions were too
imprecise to permit clear-cut conclusions to be made : no attention was
paid to the localization of the clear crescent. More recently permeability
to water has been considered by L0vtrup (1962b), but it concerns only
the egg as a whole.
VIII. Structural Organization of the Cortex
The structure of the cortex has been investigated by Dollander (1954,
1955, 1956, see also 1962) who used several techniques including the
electron microscope. A more refined electron microscopical technique
was recently used by Wartenberg and Schmidt (1960). There is good
agreement between both series of observations. Peculiar changes arise
after fertilization, but in different directions according to the taxonomic