228
JOHN RUNNSTRÖM
mostly used as the fixation liquid in the work on the cortical particles.
The question must be raised as to whether the structure of the cortical
particles is changed by the fixation. Endo (1961a) found agreement between measurements of the cortical particles carried out in the living
and fixed state. By using the freeze-drying method, Afzelius (1956)
found the appearance and dimensions of cortical particles to be similar
to those of eggs fixed in osmium tetroxide. The picture may thus reasonably well reflect the structures in living material. Motomura (1960)
insists rightly on the fact that osmium tetroxide does not preserve
mucosubstances. He, therefore, proposes fixation liquids containing cadmium in diverse combination, which should precipitate the mucosubstances. His pictures do seem, however, to contain less detail than osmium
tetroxide-fixed material.
Figure 1 gives a diagram of a cortical particle of the mature egg (see
also Endo, 1961a, text to Fig. 1). The particle is surrounded by a membrane, studied in detail by Afzelius (1956), Wolpert and Mercer (1961),
and by Endo (1961a). Its thickness seems to vary in different species
between 50 and 100 Â [see Afzelius (1956, Table II) and Endo (1961a)].
In osmium-fixed eggs of Paracentrotus
lividus, the present writer found a
thickness of about 80 Â. The double nature of the membrane came out
particularly well in a preparation of Spatangus purpureus (Afzelius) in
which two outer contours, 30 Â thick, enclosed a clearer intermediate
space, 40 Â thick. In the interior of the particle, two different components are observed. These are the lamella (Fig. 1, 1), which upon
fertilization enters the fertilization membrane, and the "extralamellar
bodies," as they may be designated. Endo called them the "hemispherical
bodies," but this designation is not suitable in all the species studied.
The extralamellar material becomes a component of the hyaline layer,
as was definitely shown by Endo (1961a); Afzelius (1956) had earlier
presented observations pointing in the same direction. The electron microscopically empty matrix may be regarded as a third interior component of the cortical particles. The cortical particles are rich in acid
polysaccharides, as was shown by Monné and Hârde (1951) and in a
more definite way by Immers (1961b) and by Aketa (1962). These acid
polysaccharides may not only be present in the organized structures of
the cortical particles, but also in the matrix. They are probably conjugated with proteins. In the following sections, cortical particles of some
sea urchins will be described in more detail.
Lönning (1963) has published micrographs showing the general structure of the cortical particles in oocytes and mature eggs of
Bnssopsis
lyrifera, an irregular sea urchin. Figure 2 represents an oblique section
through the surface layer of a mature Brissopsis egg. In the interior of
JOHN RUNNSTRÖM
mostly used as the fixation liquid in the work on the cortical particles.
The question must be raised as to whether the structure of the cortical
particles is changed by the fixation. Endo (1961a) found agreement between measurements of the cortical particles carried out in the living
and fixed state. By using the freeze-drying method, Afzelius (1956)
found the appearance and dimensions of cortical particles to be similar
to those of eggs fixed in osmium tetroxide. The picture may thus reasonably well reflect the structures in living material. Motomura (1960)
insists rightly on the fact that osmium tetroxide does not preserve
mucosubstances. He, therefore, proposes fixation liquids containing cadmium in diverse combination, which should precipitate the mucosubstances. His pictures do seem, however, to contain less detail than osmium
tetroxide-fixed material.
Figure 1 gives a diagram of a cortical particle of the mature egg (see
also Endo, 1961a, text to Fig. 1). The particle is surrounded by a membrane, studied in detail by Afzelius (1956), Wolpert and Mercer (1961),
and by Endo (1961a). Its thickness seems to vary in different species
between 50 and 100 Â [see Afzelius (1956, Table II) and Endo (1961a)].
In osmium-fixed eggs of Paracentrotus
lividus, the present writer found a
thickness of about 80 Â. The double nature of the membrane came out
particularly well in a preparation of Spatangus purpureus (Afzelius) in
which two outer contours, 30 Â thick, enclosed a clearer intermediate
space, 40 Â thick. In the interior of the particle, two different components are observed. These are the lamella (Fig. 1, 1), which upon
fertilization enters the fertilization membrane, and the "extralamellar
bodies," as they may be designated. Endo called them the "hemispherical
bodies," but this designation is not suitable in all the species studied.
The extralamellar material becomes a component of the hyaline layer,
as was definitely shown by Endo (1961a); Afzelius (1956) had earlier
presented observations pointing in the same direction. The electron microscopically empty matrix may be regarded as a third interior component of the cortical particles. The cortical particles are rich in acid
polysaccharides, as was shown by Monné and Hârde (1951) and in a
more definite way by Immers (1961b) and by Aketa (1962). These acid
polysaccharides may not only be present in the organized structures of
the cortical particles, but also in the matrix. They are probably conjugated with proteins. In the following sections, cortical particles of some
sea urchins will be described in more detail.
Lönning (1963) has published micrographs showing the general structure of the cortical particles in oocytes and mature eggs of
Bnssopsis
lyrifera, an irregular sea urchin. Figure 2 represents an oblique section
through the surface layer of a mature Brissopsis egg. In the interior of