DEVELOPMENT OF GASTROPODS
7
phospholipids about twice as high as in the rest of the egg; after its
fusion with CD the concentration of phospholipids in the CD blastomere
was 1-27 times greater than in the AB blastomere.
In Limnaea (Raven, 1945, 1946) and Succinea (Jura, 1960) the pole
plasm substance is richer in RNA than the rest of the cytoplasm.
Therefore the micromeres exhibit a stronger pyroninophily than the
macromeres. In Ilyanassa (Collier, 1960b) the concentration of RNA is
greater in AB than in CD.
Ascorbic acid in Aplysia is bound to the Golgi bodies, and shows the
same segregation as the latter (Ries, 1937) (Fig. 2). In Succinea it shows
at first a uniform distribution, then becomes concentrated in the animal
pole plasm, and follows the latter in its distribution (Jura, 1960).
The benzidine peroxidase reaction in Aplysia is at first positive in the
whole egg. With the vegetal concentration of the protein yolk, the
reaction becomes restricted to the vegetal material. Its further distribution parallels that of the protein yolk, though the enzyme is not bound
to the yolk granules (Ries, 1937, 1938).
Cytochrome oxidase in Aplysia is at first uniformly distributed, but
then it concentrates in the zone of fat droplets in the animal half of the
egg and passes mostly into the micromeres (Ries, 1937; Attardo, 1957).
In Bithynia the enzyme is restricted to the animal pole plasm, and passes
into the first and second micromeres (Attardo, 1955a). In Physa likewise
the cytochrome oxidase is more abundant in the micromeres than in the
vegetal part of the egg; later it is mainly found in the ectoderm
(Mancuso, 1955b). Presumably in all these cases the enzyme is bound to
the mitochondria, and follows their distribution.
Leucomethylene blue oxidoreductase in Aplysia is mainly found in
the animal protoplasmic area of the uncleaved egg, then in CD. After
the next cleavage the main activity is localized in C; finally, it is
especially the micromeres of the C-quadrant that give the reaction (Ries
and Gersch, 1936; Ries, 1937).
In the evaluation of these results, one of the inherent limitations of
cytochemical methods has to be taken into account. There is often no
strict proportionality between the concentration of the substance in
question and the intensity of the reaction. Presumably a certain reaction
does not, as a rule, occur at all when the intracellular concentration of
the substance is too low. These methods therefore give an exaggerated
picture of the differences in concentration. These differences generally
are relative rather than absolute, the various cells differing in the
proportions among several common substances. When this is borne in
mind, however, the results of cytochemical observations can be used as
a further clear illustration of the ooplasmic segregation taking place in
these eggs.
7
phospholipids about twice as high as in the rest of the egg; after its
fusion with CD the concentration of phospholipids in the CD blastomere
was 1-27 times greater than in the AB blastomere.
In Limnaea (Raven, 1945, 1946) and Succinea (Jura, 1960) the pole
plasm substance is richer in RNA than the rest of the cytoplasm.
Therefore the micromeres exhibit a stronger pyroninophily than the
macromeres. In Ilyanassa (Collier, 1960b) the concentration of RNA is
greater in AB than in CD.
Ascorbic acid in Aplysia is bound to the Golgi bodies, and shows the
same segregation as the latter (Ries, 1937) (Fig. 2). In Succinea it shows
at first a uniform distribution, then becomes concentrated in the animal
pole plasm, and follows the latter in its distribution (Jura, 1960).
The benzidine peroxidase reaction in Aplysia is at first positive in the
whole egg. With the vegetal concentration of the protein yolk, the
reaction becomes restricted to the vegetal material. Its further distribution parallels that of the protein yolk, though the enzyme is not bound
to the yolk granules (Ries, 1937, 1938).
Cytochrome oxidase in Aplysia is at first uniformly distributed, but
then it concentrates in the zone of fat droplets in the animal half of the
egg and passes mostly into the micromeres (Ries, 1937; Attardo, 1957).
In Bithynia the enzyme is restricted to the animal pole plasm, and passes
into the first and second micromeres (Attardo, 1955a). In Physa likewise
the cytochrome oxidase is more abundant in the micromeres than in the
vegetal part of the egg; later it is mainly found in the ectoderm
(Mancuso, 1955b). Presumably in all these cases the enzyme is bound to
the mitochondria, and follows their distribution.
Leucomethylene blue oxidoreductase in Aplysia is mainly found in
the animal protoplasmic area of the uncleaved egg, then in CD. After
the next cleavage the main activity is localized in C; finally, it is
especially the micromeres of the C-quadrant that give the reaction (Ries
and Gersch, 1936; Ries, 1937).
In the evaluation of these results, one of the inherent limitations of
cytochemical methods has to be taken into account. There is often no
strict proportionality between the concentration of the substance in
question and the intensity of the reaction. Presumably a certain reaction
does not, as a rule, occur at all when the intracellular concentration of
the substance is too low. These methods therefore give an exaggerated
picture of the differences in concentration. These differences generally
are relative rather than absolute, the various cells differing in the
proportions among several common substances. When this is borne in
mind, however, the results of cytochemical observations can be used as
a further clear illustration of the ooplasmic segregation taking place in
these eggs.