400
CH. DEVILLERS
between the cortex and the wall of the deep blastomeres (Devillers,
1948a).
Cortical resistance to dissociation increases throughout development;
when the epithelium is differentiated, the embryo becomes completely
insensible (Devillers, 1948a). A similar evolution can be observed in the
egg of Amphibia (Holtfreter, 1943a).
b. The Part Played by the Cortex in Osmoregulation
At laying, the egg undergoes a slight decrease in osmotic pressure
(Gray, 1932; Runnström, 1920; Bogucki, 1930; Svetlov, 1929) probably owing to the emission of part of its Na
+ and Ca
++ ions into the
medium (see Section III, A, 1). The osmotic pressure of the egg of
Oryzias is equivalent to that of a NaCl solution at M/7-5 (Yamamoto,
1941).
Water must be able to enter the egg in order to start activation, at
least in the case of Salmo and some others. Hence the cortex of the ripe
egg is permeable to water (and also to D 2 0) (Yagle, 1930; Manery etal.,
1935; Krogh et al, 1937; Kusa, 1951; Aoki, 1939, 1940, 1942; Kanoh,
1951, 1957; etc.) but not to colloids. Kusa suggests that there is permeability to cristalloids, but Kanoh (1957) denies it.
Nevertheless, this penetration can only last a short time (confirmed
by Prescott in Oncorhynchus, quoted by Kanoh, 1957) and it probably
does not extend further than the alveolar layer, otherwise the cytoplasm
and the yolk would be modified. The cortex becomes rapidly impermeable, thus enabling the egg to develop in a medium normally hypoor hypertonic (Aoki, 1939, 1942; Devillers et al, 1953a; Kao, 1956a; Kao
etal, 1954b; Kusa, 1951; Kanoh, 1950; Yamamoto, 1941).
A simple experiment shows this evolution of permeability during
activation in Salmo (Devillers et al, 1953a; Κ. Yamamoto, 1951, in
Oncorhynchus): the egg when laid in a NaCl solution at M/10 is not
activated (see also Kusa, 1950, in Oncorhynchus); but if it is first laid in
water (where it is activated) and taken out after 15 minutes and then
placed in M/10 NaCl, activation takes place; the short immersion in
water is sufficient to cause the onset of impermeability. In the same way,
Yamamoto (1945) activated the egg of Oryzias, by use of a detergent,
before placing it in Ringer's solution where activation occurred even
though Ringer's solution alone does not allow activation. All the
investigations on the permeability or impermeability properties of the
cortex have now brought forth a fairly coherent group of results. Gray
thought that osmoregulation was a passive phenomenon due to the
complete impermeability of the cortex, but most authors think it is an
active process (Svetlov, 1929), impermeability being neither absolute
nor invariable. Kao (1955a, b), Kao et al (1954a) and Chambers et al
CH. DEVILLERS
between the cortex and the wall of the deep blastomeres (Devillers,
1948a).
Cortical resistance to dissociation increases throughout development;
when the epithelium is differentiated, the embryo becomes completely
insensible (Devillers, 1948a). A similar evolution can be observed in the
egg of Amphibia (Holtfreter, 1943a).
b. The Part Played by the Cortex in Osmoregulation
At laying, the egg undergoes a slight decrease in osmotic pressure
(Gray, 1932; Runnström, 1920; Bogucki, 1930; Svetlov, 1929) probably owing to the emission of part of its Na
+ and Ca
++ ions into the
medium (see Section III, A, 1). The osmotic pressure of the egg of
Oryzias is equivalent to that of a NaCl solution at M/7-5 (Yamamoto,
1941).
Water must be able to enter the egg in order to start activation, at
least in the case of Salmo and some others. Hence the cortex of the ripe
egg is permeable to water (and also to D 2 0) (Yagle, 1930; Manery etal.,
1935; Krogh et al, 1937; Kusa, 1951; Aoki, 1939, 1940, 1942; Kanoh,
1951, 1957; etc.) but not to colloids. Kusa suggests that there is permeability to cristalloids, but Kanoh (1957) denies it.
Nevertheless, this penetration can only last a short time (confirmed
by Prescott in Oncorhynchus, quoted by Kanoh, 1957) and it probably
does not extend further than the alveolar layer, otherwise the cytoplasm
and the yolk would be modified. The cortex becomes rapidly impermeable, thus enabling the egg to develop in a medium normally hypoor hypertonic (Aoki, 1939, 1942; Devillers et al, 1953a; Kao, 1956a; Kao
etal, 1954b; Kusa, 1951; Kanoh, 1950; Yamamoto, 1941).
A simple experiment shows this evolution of permeability during
activation in Salmo (Devillers et al, 1953a; Κ. Yamamoto, 1951, in
Oncorhynchus): the egg when laid in a NaCl solution at M/10 is not
activated (see also Kusa, 1950, in Oncorhynchus); but if it is first laid in
water (where it is activated) and taken out after 15 minutes and then
placed in M/10 NaCl, activation takes place; the short immersion in
water is sufficient to cause the onset of impermeability. In the same way,
Yamamoto (1945) activated the egg of Oryzias, by use of a detergent,
before placing it in Ringer's solution where activation occurred even
though Ringer's solution alone does not allow activation. All the
investigations on the permeability or impermeability properties of the
cortex have now brought forth a fairly coherent group of results. Gray
thought that osmoregulation was a passive phenomenon due to the
complete impermeability of the cortex, but most authors think it is an
active process (Svetlov, 1929), impermeability being neither absolute
nor invariable. Kao (1955a, b), Kao et al (1954a) and Chambers et al