358
G.
V. LOPASHOV AND O. G.
STROEVA
cup alone (Lewis, 1905; Fischel, 1917; Lazarev, 1946; Reyer, 1950). It
is found in all these experiments that the primary size of the cornea
depends on the contact area between the surface epithelium and the
eye. If a mesenchyme layer, however thin, penetrates between them, no
corneal induction takes place.
The internal cornea of Amphibians needs the presence of the eye not
only for its origin but for the preservation of its structure during the
whole of larval life. After the removal of the eye (Lewis, 1905; Dürken,
1913; Fischel, 1917; Groll, 1923; Beliaeva, 1950) the external cornea
loses its transparency and becomes skin epidermis, with the structures
characteristic of the latter (Beliaeva, 1950). Corneal rudiments of chicks
of various age (3-4, 5-6 and 7-9 days) when cultivated on the chorioallantois (Neyfakh, 1952c) develop the more perfectly the later they
were isolated from the eye. Without the eye, they do not achieve complete differentiation, though they do not undergo a reversal of development to skin. Thus, corneal formation from surface ectoderm proceeds
in Amphibians and Birds under the influence of the eye rudiment. In
both cases the site of the appearance and the size of the cornea depend
on contact with the eye, while the completeness of the differentiation
depends on the duration of this contact. After isolation from the eye,
however, the external cornea of Amphibian tadpoles transforms into
skin, while the corneal rudiment of the chick preserves its corneal
characters.
Does the adult eye preserve its capacity to induce cornea and does the
definitive cornea require the influence of the eye to preserve its structure, as Mangold (1931) supposed on the basis of the plasticity of the
larval cornea in Amphibians? In Fishes which also keep the external
cornea in the adult this becomes pigmented and completely looses its
transparency when the eye is removed from beneath it (Harms, 1914).
On the other hand, if the whole cornea is replaced by larval skin in
Bombina bombina (Ignatieva, 1955a, b) and if a corneal area is replaced
by embryonic skin in rats (Bedniakova, 1954) and rabbits (Bedniakova,
1955; Beliaeva, 1955) the transplants, when healed, differentiate into
skin with skin glands in Amphibians and hairs in Mammals. The lack of
proper controls and of detailed histological analysis led a number of
workers (Popoff, 1948; Popoff et al., 1951a, b; Bedniakova, 1951;
Faiman, 1952; Popoff and Borsuk, 1952) to an erroneous conception
of the transformation of transplanted epidermis to cornea in adult
Amphibians, Fishes, Birds and Mammals. They assumed that cases of a
transparent regeneration of the cornea were transformations of the
transplants, On the other hand, the cornea preserved its transparency
and structure 4 months after the complete removal of the retina and lens
through an incision in the sclera in adult Bombina bombina and rats.
G.
V. LOPASHOV AND O. G.
STROEVA
cup alone (Lewis, 1905; Fischel, 1917; Lazarev, 1946; Reyer, 1950). It
is found in all these experiments that the primary size of the cornea
depends on the contact area between the surface epithelium and the
eye. If a mesenchyme layer, however thin, penetrates between them, no
corneal induction takes place.
The internal cornea of Amphibians needs the presence of the eye not
only for its origin but for the preservation of its structure during the
whole of larval life. After the removal of the eye (Lewis, 1905; Dürken,
1913; Fischel, 1917; Groll, 1923; Beliaeva, 1950) the external cornea
loses its transparency and becomes skin epidermis, with the structures
characteristic of the latter (Beliaeva, 1950). Corneal rudiments of chicks
of various age (3-4, 5-6 and 7-9 days) when cultivated on the chorioallantois (Neyfakh, 1952c) develop the more perfectly the later they
were isolated from the eye. Without the eye, they do not achieve complete differentiation, though they do not undergo a reversal of development to skin. Thus, corneal formation from surface ectoderm proceeds
in Amphibians and Birds under the influence of the eye rudiment. In
both cases the site of the appearance and the size of the cornea depend
on contact with the eye, while the completeness of the differentiation
depends on the duration of this contact. After isolation from the eye,
however, the external cornea of Amphibian tadpoles transforms into
skin, while the corneal rudiment of the chick preserves its corneal
characters.
Does the adult eye preserve its capacity to induce cornea and does the
definitive cornea require the influence of the eye to preserve its structure, as Mangold (1931) supposed on the basis of the plasticity of the
larval cornea in Amphibians? In Fishes which also keep the external
cornea in the adult this becomes pigmented and completely looses its
transparency when the eye is removed from beneath it (Harms, 1914).
On the other hand, if the whole cornea is replaced by larval skin in
Bombina bombina (Ignatieva, 1955a, b) and if a corneal area is replaced
by embryonic skin in rats (Bedniakova, 1954) and rabbits (Bedniakova,
1955; Beliaeva, 1955) the transplants, when healed, differentiate into
skin with skin glands in Amphibians and hairs in Mammals. The lack of
proper controls and of detailed histological analysis led a number of
workers (Popoff, 1948; Popoff et al., 1951a, b; Bedniakova, 1951;
Faiman, 1952; Popoff and Borsuk, 1952) to an erroneous conception
of the transformation of transplanted epidermis to cornea in adult
Amphibians, Fishes, Birds and Mammals. They assumed that cases of a
transparent regeneration of the cornea were transformations of the
transplants, On the other hand, the cornea preserved its transparency
and structure 4 months after the complete removal of the retina and lens
through an incision in the sclera in adult Bombina bombina and rats.