8
TUNEO
YAMADA
phase of primary differentiation of the neural tissue is included. The
increase of the endoplasmic reticulum is interpreted by her to be
connected with formation of tubules in the axon, and of Nissl substance
in the perikaryon.
C Golgi Complex
According to Karasaki (1959a and unpublished data) this organelle
is found in all amphibian embryonic cells so far studied. The large and
small types of the Golgi complex can be morphologically distinguished.
The large type has a total diameter of approximately 2 μ, and is found
in the vicinity of the nucleus. An array of paired lamellae each having a
total thickness of 300 Á are packed in the form of a cup which incloses
in its concavity numerous circular and oval profiles of vesicles ranging
in size from 300 to 3,000 Á. A number of vesicles are present surrounding
the structure, which are often difficult to distinguish from the smoothsurfaced cytoplasmic vesicles described above. The small type Golgi
complex is less than 1 μ in total size, and characterized by the lack of
curvature of its lamellae which form a flat sheet. Its vesicular components are smaller in size and number, compared with those of the
large type Golgi complex. According to Karasaki, at the early gastrula
stage the large type is present in the organizer cells but not in the
presumptive ectoderm cells. However, it can be detected in the presumptive neural cells of the late gastrula. On the contrary, the small
type Golgi complex is of wide occurrence in different cell-types of the
amphibian embryo, including the presumptive ectoderm cell before
contact with the organizer cells.
D. Yolk Platelets
According to Karasaki and Komoda (1958), and Karasaki (1959a)
the yolk platelets of young Triturus embryos are composed of three
parts. The bulk of the platelet is made up by the central compact part
which assumes a disc-like form having oval cross sections. Surrounding
the main body a layer of electron dense particles of ca. 100 Á diameter
is present. Further, a simple envelope of ca. 60 Á thickness, which is
observable only in early stages, invests the two parts. In thin sections
the main body shows a very regular system of fringes having a 70 Á
periodicity. A second less clear system of fringes of the same periodicity
is observable running obliquely to the first system. The periodicity of
the fringe systems observed in electron micrographs was confirmed by
electron diffraction methods. The fine structure of yolk platelets outlined above is present already in the mature oocyte (Wischnitzer, 1957),
TUNEO
YAMADA
phase of primary differentiation of the neural tissue is included. The
increase of the endoplasmic reticulum is interpreted by her to be
connected with formation of tubules in the axon, and of Nissl substance
in the perikaryon.
C Golgi Complex
According to Karasaki (1959a and unpublished data) this organelle
is found in all amphibian embryonic cells so far studied. The large and
small types of the Golgi complex can be morphologically distinguished.
The large type has a total diameter of approximately 2 μ, and is found
in the vicinity of the nucleus. An array of paired lamellae each having a
total thickness of 300 Á are packed in the form of a cup which incloses
in its concavity numerous circular and oval profiles of vesicles ranging
in size from 300 to 3,000 Á. A number of vesicles are present surrounding
the structure, which are often difficult to distinguish from the smoothsurfaced cytoplasmic vesicles described above. The small type Golgi
complex is less than 1 μ in total size, and characterized by the lack of
curvature of its lamellae which form a flat sheet. Its vesicular components are smaller in size and number, compared with those of the
large type Golgi complex. According to Karasaki, at the early gastrula
stage the large type is present in the organizer cells but not in the
presumptive ectoderm cells. However, it can be detected in the presumptive neural cells of the late gastrula. On the contrary, the small
type Golgi complex is of wide occurrence in different cell-types of the
amphibian embryo, including the presumptive ectoderm cell before
contact with the organizer cells.
D. Yolk Platelets
According to Karasaki and Komoda (1958), and Karasaki (1959a)
the yolk platelets of young Triturus embryos are composed of three
parts. The bulk of the platelet is made up by the central compact part
which assumes a disc-like form having oval cross sections. Surrounding
the main body a layer of electron dense particles of ca. 100 Á diameter
is present. Further, a simple envelope of ca. 60 Á thickness, which is
observable only in early stages, invests the two parts. In thin sections
the main body shows a very regular system of fringes having a 70 Á
periodicity. A second less clear system of fringes of the same periodicity
is observable running obliquely to the first system. The periodicity of
the fringe systems observed in electron micrographs was confirmed by
electron diffraction methods. The fine structure of yolk platelets outlined above is present already in the mature oocyte (Wischnitzer, 1957),