56
G.
REVEKBERI
long time in this state, but if fertilized, it begins to develop and as the
first step emits the two polocytes.
The eggs in some species are very clear, and no coarse granules can
be seen in them with the ordinary microscope; but in other species they
are opaque, due to the coloured granules which they possess. It is well
known that it was by following the distribution of these differently
coloured granules that Conklin (1905) was able to describe the celllineage of the larval organs ofStyela.
A. The Constituents of the Centrifuged Egg
To get an idea of the presence and the relative quantity of some
constituents of the egg one can centrifuge it, and then carry out specific
cytochemical reactions, the results of which may be advantageously
compared with observations made with the phase contrast microscope,
and the electron microscope. These techniques give good results with
Ciona eggs, as we shall demonstrate.
If observed with the ordinary light microscope, the centrifuged egg
(inside its membrane) shows five stratifications, to which correspond
five physically, chemically and optically different plasms. These plasms
are stratified on one another starting from the centripetal pole, as
follows (Mancuso, 1959a): the lipidie layer, which is very inconspicuous
and is made up of small yellow pigmented oil drops; the centripetal
hyaline layer, which is very thick and optically homogeneous though,
with a phase contrast microscope, or by cytochemical reactions, one can
distinguish some particulates; the dark layer, which is also very thick
and consists of yolk and pigment granules; the mitochondrial layer; and
the centrifugal hyaline layer, which with appropriate methods also
appears heterogeneous (Figs. 1, 2).
With the phase contrast microscope the centripetal hyaline layer is
shown to be composed of small (0*5 μ) granules which seem to be
embedded in or connected with a matrix. The centrifugal hyaline layer
also contains granules which, however, seem coarser, while in the
mitochondrial layer the mitochondria appear as spherical or elliptical
bodies (2 μ).
With the electron microscope (Mancuso, in press) the centripetal
hyaline layer is seen to consist of small spherical vesicles, with granules
at the periphery. There is no doubt that the vesicles correspond to the
endoplasmic reticulum of Palade, with its ribonucleic granules, except
that they look simpler and perhaps more primitive (Fig. 3). The
mitochondria are easily recognizable, not only by their size and elliptical
form, but especially by their structure; the cristae are not very evident,
so that the mitochondria look like those of embryonic or undetermined
G.
REVEKBERI
long time in this state, but if fertilized, it begins to develop and as the
first step emits the two polocytes.
The eggs in some species are very clear, and no coarse granules can
be seen in them with the ordinary microscope; but in other species they
are opaque, due to the coloured granules which they possess. It is well
known that it was by following the distribution of these differently
coloured granules that Conklin (1905) was able to describe the celllineage of the larval organs ofStyela.
A. The Constituents of the Centrifuged Egg
To get an idea of the presence and the relative quantity of some
constituents of the egg one can centrifuge it, and then carry out specific
cytochemical reactions, the results of which may be advantageously
compared with observations made with the phase contrast microscope,
and the electron microscope. These techniques give good results with
Ciona eggs, as we shall demonstrate.
If observed with the ordinary light microscope, the centrifuged egg
(inside its membrane) shows five stratifications, to which correspond
five physically, chemically and optically different plasms. These plasms
are stratified on one another starting from the centripetal pole, as
follows (Mancuso, 1959a): the lipidie layer, which is very inconspicuous
and is made up of small yellow pigmented oil drops; the centripetal
hyaline layer, which is very thick and optically homogeneous though,
with a phase contrast microscope, or by cytochemical reactions, one can
distinguish some particulates; the dark layer, which is also very thick
and consists of yolk and pigment granules; the mitochondrial layer; and
the centrifugal hyaline layer, which with appropriate methods also
appears heterogeneous (Figs. 1, 2).
With the phase contrast microscope the centripetal hyaline layer is
shown to be composed of small (0*5 μ) granules which seem to be
embedded in or connected with a matrix. The centrifugal hyaline layer
also contains granules which, however, seem coarser, while in the
mitochondrial layer the mitochondria appear as spherical or elliptical
bodies (2 μ).
With the electron microscope (Mancuso, in press) the centripetal
hyaline layer is seen to consist of small spherical vesicles, with granules
at the periphery. There is no doubt that the vesicles correspond to the
endoplasmic reticulum of Palade, with its ribonucleic granules, except
that they look simpler and perhaps more primitive (Fig. 3). The
mitochondria are easily recognizable, not only by their size and elliptical
form, but especially by their structure; the cristae are not very evident,
so that the mitochondria look like those of embryonic or undetermined