DEVELOPMENT OF GASTROPODS
13
In centrifugea eggs of Aplysia,
segregation of the egg substances
along the main axis takes place irrespective of the direction of stratification (Raven, 1938). Peltrera (1940) has made a special study of the
behaviour of vitamin C granules (probably bound to Golgi bodies). On
centrifugation these granules become heaped up at the centrifugal pole.
FIG. 4. Redistribution of vitamin C granules in centrifuged eggs of Aplysia limacina.
(1) Immediately after centrifugation; granules accumulated at centrifugal pole. (2-4)
Recovery of spherical shape. Granules migrate through centre of egg. (5-6) Granules
returned to their normal position in the egg (cf. Fig. 2). After Peltrera, 1940.
After the end of centrifuging they return within 5 to 20 minutes
to their normal position, forming a supra-equatorial ring as in normal
eggs (Fig. 4). In eggs centrifuged early, before the beginning of maturation, the vitamin C granules do not attain this localization at once, but
simultaneously with their segregation in uncentrifuged controls.
Another example is the animal pole plasm in Limnaea stagnalis. In
eggs centrifuged before maturation, this pole plasm forms at the normal
time, about one hour after the second maturation division, near the
original animal pole, irrespective of the direction of stratification (Raven,
1945 ; Raven and Brunnekreeft, 1951). This process takes time, however ;
a normal pole plasm is only formed when at least 2 hours have elapsed
after centrifuging.
From these observations one may conclude that the factors controlling
ooplasmic segregation are bound to some component which is not
displaced by moderate centrifuging. We know from physiological
investigations of cells that the external limiting membrane of the egg
cytoplasm and the layers situated immediately beneath it, together
forming the so-called egg cortex, exhibit a considerable degree of
rigidity. It is natural therefore to suppose that the directing factors of
13
In centrifugea eggs of Aplysia,
segregation of the egg substances
along the main axis takes place irrespective of the direction of stratification (Raven, 1938). Peltrera (1940) has made a special study of the
behaviour of vitamin C granules (probably bound to Golgi bodies). On
centrifugation these granules become heaped up at the centrifugal pole.
FIG. 4. Redistribution of vitamin C granules in centrifuged eggs of Aplysia limacina.
(1) Immediately after centrifugation; granules accumulated at centrifugal pole. (2-4)
Recovery of spherical shape. Granules migrate through centre of egg. (5-6) Granules
returned to their normal position in the egg (cf. Fig. 2). After Peltrera, 1940.
After the end of centrifuging they return within 5 to 20 minutes
to their normal position, forming a supra-equatorial ring as in normal
eggs (Fig. 4). In eggs centrifuged early, before the beginning of maturation, the vitamin C granules do not attain this localization at once, but
simultaneously with their segregation in uncentrifuged controls.
Another example is the animal pole plasm in Limnaea stagnalis. In
eggs centrifuged before maturation, this pole plasm forms at the normal
time, about one hour after the second maturation division, near the
original animal pole, irrespective of the direction of stratification (Raven,
1945 ; Raven and Brunnekreeft, 1951). This process takes time, however ;
a normal pole plasm is only formed when at least 2 hours have elapsed
after centrifuging.
From these observations one may conclude that the factors controlling
ooplasmic segregation are bound to some component which is not
displaced by moderate centrifuging. We know from physiological
investigations of cells that the external limiting membrane of the egg
cytoplasm and the layers situated immediately beneath it, together
forming the so-called egg cortex, exhibit a considerable degree of
rigidity. It is natural therefore to suppose that the directing factors of