344
G. V. LOPASHOV AND
O. G. STROEVA
(1954, 1957) that the axes of the retina emerge as follows: (1) the horizontal, i.e. anterio-posterior axis, at the stage of the early eye vesicle
(st. 21-22 in Sato, 1933, Fig. 3); (2) the vertical, i.e. dorsoventral axis,
at the stage of the early eye cup (st. 29-30 in Sato, Fig. 3). When ventral
and dorsal quadrants are exchanged up to the moment of the differentiation of either of these axes their field of vision develops according
to their new position, and not to their origin. The functional specificity
of any part of the retina, once it is determined, cannot be changed either
by joining two similar parts of the rudiment or by turning the eye
around this or any other axis (Szekely, 1954, 1957). Functional differentiation along the two mutually perpendicular axes proceeds independently in each axis (Szekely, 1954), while within each axis the
specificities of opposite quadrants are not completely independent of
each other in their formation. When a determined part of the eye was
combined in one axis with an undetermined part and the whole was
rotated, there is established a unique functional specificity along the
axis; so that if the anterior quadrant was the determined pole, then the
undetermined part differentiated as the posterior quadrant. This tendency overcomes that of the undetermined part to develop according to
its new position (Szekely, 1957).
The third, medio-lateral axis of the retina is determined later than the
first two retinal axes and independently of them. When the internal
layer of the eye of Hyla regula is turned with its internal surface outwards (Eakin, 1947), the polarity of the retina changes in accordance
with the new position, i.e., visual cells develop on the side where the
ganglion layer should have developed, and vice versa. At stage 21 (Fig.
3), just before the onset of retinal differentiation into layers, the polarity
becomes stabilized. Visual cells are always formed on the surfaces
facing internal cavities of the eye rudiment (primary eye cavity, or
accessory ones arising in the internal layer of the eye rudiment).
Earlier, mitoses had been situated on these surfaces, and the release of
the pigment granules from the retina proceeded through them (Lopashov, 1951, 1960). Apparently, the contact with the fluid of the internal
medium of the retina contributes to the development of the visual layer
and is thus one of the factors determining the polarity of the retina.
Thus, by the time of onset of retinal differentiation into layers, all three
axes characterizing its functional specificity are already established.
The complex of phenomena analysed above plays the main role in the
primary segregation of the eye rudiment. Most of these phenomena
proceed in close interconnection, mutually strengthening or excluding
each other, which leads to a progressive augmentation of differences
between the parts into which the rudiment segregates. Accumulation of
eye rudiment cells, resulting in the development of the retina, increases
G. V. LOPASHOV AND
O. G. STROEVA
(1954, 1957) that the axes of the retina emerge as follows: (1) the horizontal, i.e. anterio-posterior axis, at the stage of the early eye vesicle
(st. 21-22 in Sato, 1933, Fig. 3); (2) the vertical, i.e. dorsoventral axis,
at the stage of the early eye cup (st. 29-30 in Sato, Fig. 3). When ventral
and dorsal quadrants are exchanged up to the moment of the differentiation of either of these axes their field of vision develops according
to their new position, and not to their origin. The functional specificity
of any part of the retina, once it is determined, cannot be changed either
by joining two similar parts of the rudiment or by turning the eye
around this or any other axis (Szekely, 1954, 1957). Functional differentiation along the two mutually perpendicular axes proceeds independently in each axis (Szekely, 1954), while within each axis the
specificities of opposite quadrants are not completely independent of
each other in their formation. When a determined part of the eye was
combined in one axis with an undetermined part and the whole was
rotated, there is established a unique functional specificity along the
axis; so that if the anterior quadrant was the determined pole, then the
undetermined part differentiated as the posterior quadrant. This tendency overcomes that of the undetermined part to develop according to
its new position (Szekely, 1957).
The third, medio-lateral axis of the retina is determined later than the
first two retinal axes and independently of them. When the internal
layer of the eye of Hyla regula is turned with its internal surface outwards (Eakin, 1947), the polarity of the retina changes in accordance
with the new position, i.e., visual cells develop on the side where the
ganglion layer should have developed, and vice versa. At stage 21 (Fig.
3), just before the onset of retinal differentiation into layers, the polarity
becomes stabilized. Visual cells are always formed on the surfaces
facing internal cavities of the eye rudiment (primary eye cavity, or
accessory ones arising in the internal layer of the eye rudiment).
Earlier, mitoses had been situated on these surfaces, and the release of
the pigment granules from the retina proceeded through them (Lopashov, 1951, 1960). Apparently, the contact with the fluid of the internal
medium of the retina contributes to the development of the visual layer
and is thus one of the factors determining the polarity of the retina.
Thus, by the time of onset of retinal differentiation into layers, all three
axes characterizing its functional specificity are already established.
The complex of phenomena analysed above plays the main role in the
primary segregation of the eye rudiment. Most of these phenomena
proceed in close interconnection, mutually strengthening or excluding
each other, which leads to a progressive augmentation of differences
between the parts into which the rudiment segregates. Accumulation of
eye rudiment cells, resulting in the development of the retina, increases