THE MORPHOGENETIC ROLE OF THE CORTEX
OF THE AMPHIBIAN EGG
JEAN J. PASTEELS
Laboratoire d
y
Anatomie et d'Embrologie humaines, Université libre de
Bruxelles, Belgium.
I. Introduction
JJ63
II. Cortex and Bilateral Symmetry
3 6
4
III. Grey Crescent and'Cortical Field'
3 6
8
IV. Born's Crescent, or an Artificial'Grey Crescent'
3 7
4
V. Grafting of Cortex Material
3
8
VI. Separation of Blastomeres by Ligature
3 8
0
VII. Cortical Field and Permeability
3 8
3
VIII. Structural Organization of the Cortex
3 8
4
IX. The 'Coat'ofHoltfreter
6
X. Summary and Conclusions
3
^
References
7
I. Introduction
Many embryologists agree that the cortex of the egg is one of the most
important agents in primary development. Polarity as well as dorsoventral organization have been related to gradients or fields depending
upon the cortical structure; these structures may eventually interact
with the inner cytoplasm (or yolk) to induce epigenesis of development
(see Schleip, 1929; Dalcq, 1941 ; Dalcq and Pasteels, 1937, 1938; Raven,
1958).
At first sight, these 'cortical' theories of development seem to suffer
from a serious drawback : the main argument in favour of them is the
impossibility that any inner structure can resist a severe centrifugation,
which is known in most cases to allow perfect morphogenesis.
This has recently lead to some criticism by Mercer and Wolpert
(1962), on the basis that if the egg of the sea urchin Psammechinus
is
centrifuged at 4,400 g for 5 minutes and then fixed immediately, the
only structure not affected by this treatment is the plasma membrane
(or plasmalemma). Mercer and Wolpert conclude that 'the problem of
the cortex in relation to . . . the seat of the egg's polarity is equivocal
and requires further investigation'. It is obvious that more direct
evidence is needed to solve the problem of the morphogenetic role of the
cortex. The sea urchin egg has offered no such evidence so far. On the
other hand, numerous investigations in either normal or experimental
363
OF THE AMPHIBIAN EGG
JEAN J. PASTEELS
Laboratoire d
y
Anatomie et d'Embrologie humaines, Université libre de
Bruxelles, Belgium.
I. Introduction
JJ63
II. Cortex and Bilateral Symmetry
3 6
4
III. Grey Crescent and'Cortical Field'
3 6
8
IV. Born's Crescent, or an Artificial'Grey Crescent'
3 7
4
V. Grafting of Cortex Material
3
8
VI. Separation of Blastomeres by Ligature
3 8
0
VII. Cortical Field and Permeability
3 8
3
VIII. Structural Organization of the Cortex
3 8
4
IX. The 'Coat'ofHoltfreter
6
X. Summary and Conclusions
3
^
References
7
I. Introduction
Many embryologists agree that the cortex of the egg is one of the most
important agents in primary development. Polarity as well as dorsoventral organization have been related to gradients or fields depending
upon the cortical structure; these structures may eventually interact
with the inner cytoplasm (or yolk) to induce epigenesis of development
(see Schleip, 1929; Dalcq, 1941 ; Dalcq and Pasteels, 1937, 1938; Raven,
1958).
At first sight, these 'cortical' theories of development seem to suffer
from a serious drawback : the main argument in favour of them is the
impossibility that any inner structure can resist a severe centrifugation,
which is known in most cases to allow perfect morphogenesis.
This has recently lead to some criticism by Mercer and Wolpert
(1962), on the basis that if the egg of the sea urchin Psammechinus
is
centrifuged at 4,400 g for 5 minutes and then fixed immediately, the
only structure not affected by this treatment is the plasma membrane
(or plasmalemma). Mercer and Wolpert conclude that 'the problem of
the cortex in relation to . . . the seat of the egg's polarity is equivocal
and requires further investigation'. It is obvious that more direct
evidence is needed to solve the problem of the morphogenetic role of the
cortex. The sea urchin egg has offered no such evidence so far. On the
other hand, numerous investigations in either normal or experimental
363