346
G. V. LOPASHOV AND O. G.
STROEVA
behaviour of the two layers is due to the fact that mitoses cease in the
pigmented epithelium by the 4th day of incubation, while the retina
increases up to the 15th day by augmentation of cells in the ciliary
zone (Coulombre, 1955). It follows from this that the increase of the
area of the pigment epithelium becomes dependent much earlier than
that of the retina on the operation of tangential forces. These latter
arise in the course of development due to the increasing intraocular
pressure. Under its action the further increase of area, progressive
decrease of thickness and harmonious growth of both layers take
place (Coulombre, 1956). In the mammalian eye, the external layer of
which still preserves its capacity to transform into retina at the
time of the onset of its pigmentation and of the closure of the choroid
fissure, delay in development of intraocular pressure leads to the
appearance of retina in the external layer (Stroeva, 1960). This is due
to the fact that in Mammals the action of the mesenchyme on the external layer depends on the stretching of the latter to a unicellular layer
to a greater extent than in other forms. Some areas of the external layer,
in particular those along the margin of the choroid fissure and of the
lens, remain multilayered. Then, in the absence of intraocular pressure
(for example, if the choroid fissure has not closed), they remain aggregated and differentiate into retina (Stroeva, 1960). Such changes in the
differentiation of the external layer lead to congenital malformations of
the eye in animals and humans, the typical and atypical colobomas of
the retina and the choroid coat. There exists at present a hypothesis
(Mann, 1957; Dejean, Leplat and Hervouét, 1958; Giroud et al., 1954;
Giroud, 1957) which regards the appearance of the retina in the external
layer in colobomas as a consequence of the turning outwards of the
internal layer through the open choroid fissure. This hypothesis has to
be replaced by a conception based on the experiments presented here.
Formation of the ciliary body also depends on intraocular pressure.
The undifferentiated margin of the eye cup in chicks becomes closely
attached to the equator of the lens on the 4th day of incubation
(Coulombre, 1955). The area of the presumptive ciliary body grows intensively up to the 8th day. When intraocular pressure is eliminated on
the 4th day of incubation, the ciliary body remains much thickened and
subdivides into a small number of thick and disorientated folds. No
asymmetry of the ciliary body develops. After a temporary elimination
of the intraocular pressure, the ciliary body is normally formed, but
possesses a reduced number of ciliary folds (Coulombre and Coulombre,
1957). The authors suppose that, among other factors, formation of the
ciliary body is a function of the interrelation between intraocular
pressure (which contributes to the thinning and extension of the
ciliary zone), and the differential alteration of the rigidity of the
G. V. LOPASHOV AND O. G.
STROEVA
behaviour of the two layers is due to the fact that mitoses cease in the
pigmented epithelium by the 4th day of incubation, while the retina
increases up to the 15th day by augmentation of cells in the ciliary
zone (Coulombre, 1955). It follows from this that the increase of the
area of the pigment epithelium becomes dependent much earlier than
that of the retina on the operation of tangential forces. These latter
arise in the course of development due to the increasing intraocular
pressure. Under its action the further increase of area, progressive
decrease of thickness and harmonious growth of both layers take
place (Coulombre, 1956). In the mammalian eye, the external layer of
which still preserves its capacity to transform into retina at the
time of the onset of its pigmentation and of the closure of the choroid
fissure, delay in development of intraocular pressure leads to the
appearance of retina in the external layer (Stroeva, 1960). This is due
to the fact that in Mammals the action of the mesenchyme on the external layer depends on the stretching of the latter to a unicellular layer
to a greater extent than in other forms. Some areas of the external layer,
in particular those along the margin of the choroid fissure and of the
lens, remain multilayered. Then, in the absence of intraocular pressure
(for example, if the choroid fissure has not closed), they remain aggregated and differentiate into retina (Stroeva, 1960). Such changes in the
differentiation of the external layer lead to congenital malformations of
the eye in animals and humans, the typical and atypical colobomas of
the retina and the choroid coat. There exists at present a hypothesis
(Mann, 1957; Dejean, Leplat and Hervouét, 1958; Giroud et al., 1954;
Giroud, 1957) which regards the appearance of the retina in the external
layer in colobomas as a consequence of the turning outwards of the
internal layer through the open choroid fissure. This hypothesis has to
be replaced by a conception based on the experiments presented here.
Formation of the ciliary body also depends on intraocular pressure.
The undifferentiated margin of the eye cup in chicks becomes closely
attached to the equator of the lens on the 4th day of incubation
(Coulombre, 1955). The area of the presumptive ciliary body grows intensively up to the 8th day. When intraocular pressure is eliminated on
the 4th day of incubation, the ciliary body remains much thickened and
subdivides into a small number of thick and disorientated folds. No
asymmetry of the ciliary body develops. After a temporary elimination
of the intraocular pressure, the ciliary body is normally formed, but
possesses a reduced number of ciliary folds (Coulombre and Coulombre,
1957). The authors suppose that, among other factors, formation of the
ciliary body is a function of the interrelation between intraocular
pressure (which contributes to the thinning and extension of the
ciliary zone), and the differential alteration of the rigidity of the