VITELLINE MEMBRANE AND CORTICAL PARTICLES 309
are entangled in the coat. Polyspermy is common. The results agree thus
with those obtained by Okazaki (1956).
The experiments referred to indicate that energy-rich compounds,
perhaps ATP, are involved in the cortical changes following upon
fertilization (or artificial parthenogenesis). In the experiment referred
to, DNP could have an activating effect on an ATPase ; in this way ATP
would be gradually broken down, so that the content of available ATP
would not suffice to provide the energy necessary for the cortical changes.
Okazaki (1956) points, however, to one difficulty; added ATP is not
able to remove the effect of DNP. He points out that this may be due
to inpermeability of the egg surface. Runnström and Kriszat (1950a)
pretreated unfertilized eggs of Psammechinus
miliaris with 3 X 10~
3 M
ATP in sea water for 60 min and then diluted the medium by addition
of twice-distilled water. Despite the hypotonicity of the medium the eggs
broke up very slowly and only in one spot, from which a very limited
amount of inner material escaped. The eggs in the hypotonic medium
were surrounded by a rather refractive membrane. In several places single
cortical lamellae could be perceived in the membrane; in other places
the incorporation of the lamellae was denser. It is evident that the cortical particles have opened up under the joint effect of ATP and hypotonicity. In contrast, the nonpretreated eggs broke up soon and most of
the cytoplasm flowed out and left a large, apparently empty space below
the thin vitelline membrane. Some cortical lamellae may have entered the
membrane also here, but in comparison with ATP-treated eggs the vitelline membrane received very little lamellar material. Similar results were
obtained by Wicklund (1947) with eggs of Arbacia
lixula.
Unfertilized eggs immersed in hypotonic medium serve in a way as a
"cell model" in the sense of the workers on muscle (Weber and Portzehl, 1954). The procedure removes the permeability barrier, and the
test agent is thus able to penetrate to its site of action. The action of
ATP and Ca
2+ on the egg model brought about the formation of a membrane similar to the fertilization membrane. Moreover, the cytoplasm
changed to a more homogeneous texture similar to that after fertilization.
The effect of DNP on the unfertilized eggs is reversible, as Okazaki
(1956) showed. The reversion may mean that even in the unfertilized
egg ATP could be formed. Lindberg (1950) demonstrated that in the
unfertilized egg of Paracentrotus
lividus only a rather thin layer, which
may correspond to the cortical layer, is accumulating ATP. The store of
triphosphates in the egg is rather high (see T. Hultin, 1957). There may
be a compartmentation in the egg with respect to ATP, only a limited
amount of this substance being available for the cortical changes.
are entangled in the coat. Polyspermy is common. The results agree thus
with those obtained by Okazaki (1956).
The experiments referred to indicate that energy-rich compounds,
perhaps ATP, are involved in the cortical changes following upon
fertilization (or artificial parthenogenesis). In the experiment referred
to, DNP could have an activating effect on an ATPase ; in this way ATP
would be gradually broken down, so that the content of available ATP
would not suffice to provide the energy necessary for the cortical changes.
Okazaki (1956) points, however, to one difficulty; added ATP is not
able to remove the effect of DNP. He points out that this may be due
to inpermeability of the egg surface. Runnström and Kriszat (1950a)
pretreated unfertilized eggs of Psammechinus
miliaris with 3 X 10~
3 M
ATP in sea water for 60 min and then diluted the medium by addition
of twice-distilled water. Despite the hypotonicity of the medium the eggs
broke up very slowly and only in one spot, from which a very limited
amount of inner material escaped. The eggs in the hypotonic medium
were surrounded by a rather refractive membrane. In several places single
cortical lamellae could be perceived in the membrane; in other places
the incorporation of the lamellae was denser. It is evident that the cortical particles have opened up under the joint effect of ATP and hypotonicity. In contrast, the nonpretreated eggs broke up soon and most of
the cytoplasm flowed out and left a large, apparently empty space below
the thin vitelline membrane. Some cortical lamellae may have entered the
membrane also here, but in comparison with ATP-treated eggs the vitelline membrane received very little lamellar material. Similar results were
obtained by Wicklund (1947) with eggs of Arbacia
lixula.
Unfertilized eggs immersed in hypotonic medium serve in a way as a
"cell model" in the sense of the workers on muscle (Weber and Portzehl, 1954). The procedure removes the permeability barrier, and the
test agent is thus able to penetrate to its site of action. The action of
ATP and Ca
2+ on the egg model brought about the formation of a membrane similar to the fertilization membrane. Moreover, the cytoplasm
changed to a more homogeneous texture similar to that after fertilization.
The effect of DNP on the unfertilized eggs is reversible, as Okazaki
(1956) showed. The reversion may mean that even in the unfertilized
egg ATP could be formed. Lindberg (1950) demonstrated that in the
unfertilized egg of Paracentrotus
lividus only a rather thin layer, which
may correspond to the cortical layer, is accumulating ATP. The store of
triphosphates in the egg is rather high (see T. Hultin, 1957). There may
be a compartmentation in the egg with respect to ATP, only a limited
amount of this substance being available for the cortical changes.