IX. DEVELOPMENT OF THE TELEOSTEAN EGG
401
(1951) thus observed a swelling of the egg of Fundulus in a sucrose
solution; slight currents of endo- and exosmosis are seen in the egg of
Oryzias (Yamamoto, 1941) or of Oncorhynchus (Kanoh, 1952c, 1957),
placed in an anisotonic solution (hypo- or hypertonic) unbalanced or
not; vital stains penetrate. To these observations one can object that
permeability is not normal (see Section III, C, 2, a) since these media
can alter the cortex, perhaps reversibly. Thus vital stains that do not
disturb development cause a cortical stiffening which becomes apparent
by a change in shape, a flattening of the blastoderm (unpublished observations : see also Runnström and Kriszat, 1957, on the sea-urchin egg).
If permeability implies the coexistence of two mechanisms (see
indications on the structure of the cortex in Kao, 1956b and Ussing,
1952)—one of diffusion, the other of filtration through the pores—media
other than water could widen the pores momentarily and create an
abnormal structure.
Normal conditions of development require a cortical impermeability
(not absolute) to protect the cellular contents against the medium's
cytolizing action, for all the other walls of the blastomeres are permeable to water. One can even wonder if this impermeability does not
play a part in organogenesis by maintaining inside the egg the 'substances' elaborated during differentiation. For if the gastrula explants
are deprived of their enveloping layer before being cultivated (Devillers
et al., 1957b; see also Section IV, B) the degree of differentiation of the
main structures is much weaker than that of intact explants. Might
not this feeble differentiation be due to the escape of 'morphogenetic
substances' into the medium, as observed by Niu and Twitty (1953) with
cells of Amphibia deprived of the coat?
c. Adhesivity
I have examined this in an earlier review (Devillers, 1955).
d. Mechanical Properties
In a physiological solution the evolution of a wound in the cortex of
the undivided egg can be compared to that described by Holtfreter
(1943a) in the egg of Amphibia; at first, the opening widens and becomes
circular; then the lips of the wound contract and close up. The behaviour
of coloured marks, or of bits of charcoal placed around the lesion show
that healing is really due to a cortical expansion, and not to a neoformation of membrane (Devillers, 1948a; Trinkaus, 1948, 1949b) (Fig. 12).
The first movement of enlargement would merely represent the retraction of an elastic membrane distended by the cell contents. Against
this interpretation, Trinkaus (1951) puts forward the following experiment : a large wound is made in the perivitelline cortex of Fundulus and
401
(1951) thus observed a swelling of the egg of Fundulus in a sucrose
solution; slight currents of endo- and exosmosis are seen in the egg of
Oryzias (Yamamoto, 1941) or of Oncorhynchus (Kanoh, 1952c, 1957),
placed in an anisotonic solution (hypo- or hypertonic) unbalanced or
not; vital stains penetrate. To these observations one can object that
permeability is not normal (see Section III, C, 2, a) since these media
can alter the cortex, perhaps reversibly. Thus vital stains that do not
disturb development cause a cortical stiffening which becomes apparent
by a change in shape, a flattening of the blastoderm (unpublished observations : see also Runnström and Kriszat, 1957, on the sea-urchin egg).
If permeability implies the coexistence of two mechanisms (see
indications on the structure of the cortex in Kao, 1956b and Ussing,
1952)—one of diffusion, the other of filtration through the pores—media
other than water could widen the pores momentarily and create an
abnormal structure.
Normal conditions of development require a cortical impermeability
(not absolute) to protect the cellular contents against the medium's
cytolizing action, for all the other walls of the blastomeres are permeable to water. One can even wonder if this impermeability does not
play a part in organogenesis by maintaining inside the egg the 'substances' elaborated during differentiation. For if the gastrula explants
are deprived of their enveloping layer before being cultivated (Devillers
et al., 1957b; see also Section IV, B) the degree of differentiation of the
main structures is much weaker than that of intact explants. Might
not this feeble differentiation be due to the escape of 'morphogenetic
substances' into the medium, as observed by Niu and Twitty (1953) with
cells of Amphibia deprived of the coat?
c. Adhesivity
I have examined this in an earlier review (Devillers, 1955).
d. Mechanical Properties
In a physiological solution the evolution of a wound in the cortex of
the undivided egg can be compared to that described by Holtfreter
(1943a) in the egg of Amphibia; at first, the opening widens and becomes
circular; then the lips of the wound contract and close up. The behaviour
of coloured marks, or of bits of charcoal placed around the lesion show
that healing is really due to a cortical expansion, and not to a neoformation of membrane (Devillers, 1948a; Trinkaus, 1948, 1949b) (Fig. 12).
The first movement of enlargement would merely represent the retraction of an elastic membrane distended by the cell contents. Against
this interpretation, Trinkaus (1951) puts forward the following experiment : a large wound is made in the perivitelline cortex of Fundulus and